Republican vice presidential candidate Mike Pence speaks on his cell phone following the US vice presidential debate at Longwood University in Farmville, Virginia on October 4, 2016. / AFP / SAUL LOEB (Photo credit should read SAUL LOEB/AFP/Getty Images)

So gently did Mike Pence throw Donald Trump under the bus on Tuesday night that the treadmarks on Trump's forehead barely showed. But Pence's bus was moving at warp speed when it mowed down Ted Cruz.

Observers may be forgiven for thinking that this debate was about 2016. Pence, after all, is Trump's running mate, charged with helping him seize the White House. But his real mission was more subtle: to play the loyal Republican soldier while decorously avoiding the -- perhaps impossible -- task of defending Trump's words and deeds.

The goal of this exercise was to embody for the GOP base what Trump is not -- a conventional evangelical conservative who embodies all things good and true. This, some thought, was intended make it easier for restive Republicans to support their erratic nominee. But the effect was to evoke the wistful thought among the faithful that the nominee should be Pence himself. This moment of rue, no doubt, was meant to inspire a collective stirring of hope: ah, but there's always 2020...

Somewhere in Texas, Cruz felt the bus hit him.

This was no accident -- it was vehicular manslaughter, aimed straight at Cruz's plans for the future. By playing the loyal soldier, Pence cast Cruz as the self-serving freelancer, posing as the conscience of conservatism while moving from one calculation to the next.

To the surprise and disappointment of many on the Republican right, Cruz recently endorsed Trump. To put it kindly, this distress at his volte-face suggests a certain naïveté about Cruz's essential nature. Still, on this occasion his elasticity and opportunism were particularly striking.

After all, it was Trump who called Cruz "Lyin' Ted"; used Cruz's Canadian birth to challenge his eligibility to be president; mocked his wife's appearance; and suggested that his father was involved in the assassination of John F. Kennedy. And it was Cruz who, after months of heaping praise on Trump in the hope of inheriting his followers, called Trump "a pathological liar"; "utterly amoral"; "a serial philanderer"; and "a narcissist at a level I don't think this country has ever seen", then refused to endorse Trump at the GOP convention -- as a matter of "conscience," of course.

But Cruz's conscience, he would have us believe, is ever at work. And so in late September, citing "many months of careful consideration, of prayer and searching my own conscience," Cruz declared, "I will vote for the Republican nominee, Donald Trump."

Cynics suggested that this political jiu-jitsu was less a matter of soul-scouring then a gimlet eyed appraisal of his own self-interest. As Pence's debate performance suggests, Cruz is hardly alone. Though Donald Trump is far from dead, for a select group of Republicans the body is already cooling. The only question is how much lip service they will pay to the corpse.

This is a complex calculation for each and all. The Trump candidacy exposes the GOP's grievous fractures; his defeat would further aggravate them in unpredictable but surely damaging ways which will be difficult to navigate. For the hopefuls of 2020, more bars their path to the White House than the specter of President Hillary Clinton -- or even each other. Simply winning the nomination may be, in itself, near fatal.

The GOP's factions are not only it odds with each other, but all too often with the general electorate. The more support they give to a prospective nominee, the more they damage that candidate in November 2020.

Take the evangelicals -- a target for Pence, Cruz and pretty much everyone else. With the ferocity of dead-enders, they insist on blanket opposition to abortion, even in the case of rape or incest. They oppose gay rights in every area of life, including marriage and freedom from discrimination. They are obsessed with bathroom use by LGBT Americans. In the name of religious freedom, they want to tear down the wall between church and state. But where they have stuck their flag in the ground, shouting defiance, the larger society is passing them by on the path to greater tolerance.

Or the Tea Party crowd. Driven by fury and a sense of betrayal, they rail against government and the congressional leaders of their own party, killing off John Boehner and subjecting Paul Ryan to frequently impotent misery. Such is their nihilism that they would rather shut down the government -- forcing the rest of us to live with whatever may follow -- than pursue a program which, however conservative, offends their sense of purity. These folks live in a very special world. Most Americans do not.

Including another influential element of the GOP -- its donor base and the Chamber of Commerce crowd, devotees of lower taxes, deregulation and free trade agreements. These programs depend on the GOP winning the White House and enacting legislation and, therefore, on a modicum of pragmatism. This, to put it mildly, is not the Tea Party model.

Nor is it the wish list of the Republican base among the embattled middle and working classes. Trump activated their suspicion of free trade and globalization -- and of those within the party who advocate tax cuts, entitlement reform and free market ideology. Their desires cannot be reconciled; their differences with privileged Republicans will not be easy for the hopefuls to gloss over.

So, too, with the nativism, racial resentment and anti-immigrant feeling essential to Trump's candidacy. This deeply emotional issue separates the base from the Republican establishment and, more fatally, from the larger electorate, including traditional Republicans among educated and suburban whites who want a humane and reasonable solution to the problems of illegal immigration. As Trump is currently proving, this agenda may well be a demographic poison pill -- indispensable to his success in Republican primaries, and increasingly fatal in a general election.

Finally, Trump has exposed the conflict between his "America First" xenophobia and Republican hawks and internationalists. He garnered support from Republicans, often blue-collar folks, who were fearful of terrorism, suspicious of all Muslims, and sick of wars in which their kids suffered more than the children of Americans at large.

In contrast, Trump was roundly rejected by the party's foreign-policy establishment, who regard America as essential to preserving global order and aggressively combating Islamic terrorists -- not by mindlessly restricting immigration, but by using military power. But among Americans at large, weary of war and fed up with its costs, Trump's neo-isolationism holds instinctive appeal. Here, too, the clash of contending forces among Republicans has broader electoral implications for the party, and for its perspective nominees.

For if the GOP loses in November, all this raises an existential question: what is the meaning of Trump?

The components of this question are complex. Among the base and within the party, what loyalty to Trump will remain? Will there be Trumpism without Trump? If so, which of its elements -- including a hard line on immigration, an embrace of protectionism, and a pseudo-populist aversion to the GOP elite and its agenda -- will still be potent in the primary contest of 2020? And at what cost in the general election?

For the aspiring nominees, this is a strategic and tactical Rubik's cube, requiring a series of nice calculations with dubious outcomes. And each maneuver will be shadowed by this ominous thought: is the party so riven by conflict and contradictions that victory within the party, however attained, means doom in November?

In short, absent a national cataclysm is the GOP as currently constituted still viable in presidential elections? Or must it reinvent itself in a form so different -- and so remote from its current circumstances -- that none of these candidates will resemble a successful Republican nominee of the future?

Viewed from this perspective, the maneuverings of the 2020 wannabes may wind up resembling the meanderings of men lost in a maze from which there is no escape, moving this way and that in the deluded belief that somewhere ahead lies daylight.

Granted, seeing Ted Cruz in in this light affords a certain pleasure -- no pretender is more obviously calculating than the dank Prince of Darkness. And so it is darkly amusing to imagine him making another series of self-serving calculations -- relentlessly stabbing others in the back while pretending to lonely nobility -- all of which are destined to be pointless.

As they were in 2016, where his cleverness produced a sequence of self-inflicted wounds which doomed him then, and will dog him going forward.

To start, he cast himself as a tribune of the Tea Party, precipitating a government shutdown which earned him the deep loathing of the party's establishment and business classes. Particularly striking was his gleeful castigation of Republican congressional leaders as cowards, sellouts, and establishment tools -- not every freshman senator calls Mitch McConnell a liar. During the primary season, many prominent Republicans -- while despising both -- actually considered Cruz more odious than Trump. In itself, this was deadly.

A second misstep was his strident embrace of retrograde social conservatism, angling to make evangelicals a key part of his base. This put off Republicans looking, at least, for a gentler tone. And even among fundamentalists, it did not work. When Trump stole them in droves, sweeping the southern primaries, Cruz was the walking dead. His subsequent decimation in New England, New York and the mid-Atlantic states exposed the narrowness of his far-right appeal.

Faux-clever, as well, was his attempt to glide in Trumps nativist slipstream, embracing his anti-Muslim and anti-immigrant rhetoric in the transparent hope of inheriting his voters. What he inherited was a trace of Trump's aroma.

So how does he modify these positions? He can't. Going forward he can tinker around the margins, trying to pacify some of Trump's base by flirting with economic populism and rejecting "nation building." But Cruz's chosen persona is the courageous man of principle; his electoral rationale, however dubious, is that the GOP can only win by nominating a really, truly true conservative who embraces timeless verities. Shed this identity, and all that is left is Cruz, naked in his ambition. As his latest reversal demonstrates, this is not a pretty picture.

Both ambition and calculation were on ample display at this year's convention, along with his trademark aggression. Like many ambitious Republicans, Pence clambered on board with painful alacrity. Other Republicans opposed to Trump -- John Kasich leaps to mind -- at least hewed to political decorum. Only Cruz chose to be the sanctimonious skunk at Trump's garden party, showing up to deliver a self-aggrandizing speech about political conscience, climaxed by his all-too-showy refusal to endorse.

In the near term he got what he thought he wanted -- a heroic pose, a cascade of boos, and the role of prophet with honor who would reintroduce a grateful party to its soul. But then unpleasant realities started presenting themselves -- his donors were flocking to Trump, party loyalists were angry, and he had to win reelection to the Senate in 2018.

Thus his ever-deployable conscience struck yet again, compelling him to fall in line behind Trump. And so he got the worst of both worlds -- a stand on principle which proved transient, alienating Republicans on all sides who see Cruz as The Lone Stranger, forever out for himself.

That's the ultimate problem -- Cruz himself. As a man, he has the oleaginous manner of a self-serving televangelist, complete with overdone histrionics and an aura of sincerity which is transparently insincere. As a politician, he is everything most Americans do not want -- a fundamentalist, climate-denying, reactionary, demagogic dead-ender. The only question is who gets to kill him off first -- his own party, or Americans at large.

Or, perhaps, Mike Pence. As a politician, Pence is much better than Cruz at faking humility while embodying religiosity and party loyalty. His obeisance to Trump may smack of grubby ambition but, to many Republicans, it embodies their ultimate principle: any Democratic president is bad, and Hillary Clinton is outright evil. This simplifies matters a lot.

The Pence persona is simple indeed -- perhaps too simple for the country at large. He is not simply a social conservative, but an evangelical diehard.

Take abortion. In Congress he led the fight to defund Planned Parenthood. While Governor of Indiana, he signed an law so strict that it barred abortion even in cases of genetic abnormalities, while targeting doctors who performed them. No matter to Pence that the law was struck down, as he surely knew it would be.

Or LGBT rights. As a congressman, he opposed federal funding to treat HIV/AIDS, unless the government funded programs to discourage same-sex relationships. A nasty side effect of his policies in Indiana -- closing Planned Parenthood clinics and opposing needle exchanges -- was to provoke a county-wide AIDS epidemic.

Most notoriously, he spearheaded a law to protect businesses which refused service to LGBT people on religious grounds. Although protests from the business community forced him to back down, he had once more played to his audience -- people who think like he does.

And what he thinks is so narrow as to redefine the word "provincial." He has denied that smoking causes cancer. He questions climate change and the theory of evolution. He is a poster boy for the NRA who opposes background checks. He tried to bar Syrians from coming to Indiana until stopped by a panel of three Republican judges. For Pence, there is no right-wing nostrum too short-sighted to embrace.

Perhaps the cul-de-sac of his mind is a happy place to be. But most Americans don't live there, and young Americans don't want to. Pence's beliefs are not theirs.

Which brings us to a man forever searching for his beliefs: the human windsock known as Marco Rubio. When the wind stops blowing, the sock is empty.

In 2016, Rubio proved to be less candidate than concept: a glib young Hispanic who could personify the future without saying what it was. On the stump he molded himself into a right-wing cyborg, programmed to recite talking points while attacking Barack Obama with the near-comical ferocity of a chihuahua barking through a screen door. The whole idea, it seemed, was to exemplify great Republican horseflesh.

So instead of substance, Rubio offered us... himself. His campaign came to resemble a political Groundhog's Day, a perpetual Fourth of July featuring a touching origin speech -- complete with humble parents who achieved the American Dream -- delivered so well that tears welled in the eyes. Until one had heard it for the 50th time.

But who was Rubio, really? Sadly, this -- a too young man in far too big a hurry, forever shape-shifting in his restless drive for the ultimate prize. His indifference to the Senate as anything but launching pad betrayed the shallowness beneath the speechifying. Climbing, it seemed, was the only meaning of Rubio's American dream.

His political career was ever thus. As a Florida legislator, he embraced green energy; as a presidential candidate, he virtually coined the "I'm not a scientist" dodge to deny the reality of climate change which, ironically, is an existential threat to the Florida coastline. As a candidate for Senate, he took a hard-line on immigration reform; as a budding presidential aspirant, he became a leading sponsor of an immigration reform bill. Until, confronted with the anger of the base, he abruptly sold out his cosponsors and turned against his own bill.

There was no Rubio constituency, it turned out, because there was no real Rubio. His most consistent role was that of political pet to plutocrats, a vacuum for soft money given by imperious men who expect a return on their investment. A case in point is Sheldon Adelson, the far-right casino magnate who, according to insiders, Rubio called constantly for advice on who to be.

Adelson is an implacable Zionist who thinks God gave Israel the West Bank; in yet another change of position, Rubio kicked the two-state solution to the curb. Adelson is pushing a bill to hamstring internet gambling; Rubio signed on as co- sponsor. Adelson hates the Iran deal; Rubio vowed to rip it up.

Indeed, Rubio financed his presidential campaign chiefly through soft money, much of it from undisclosed sources. Rubio insists he is not for sale, but he is clearly open to long-term rentals. His hawkishness on foreign policy seemed calculated to please billionaire donors like Adelson, Norman Braman and Paul Singer, all anti-tax, pro-Israel hardliners. As did his economic program, featuring enormous tax cuts for the rich which were certain, in the estimate of independent experts, to bust the deficit wide open.

As a candidate, his hollowness showed. Pressured in debate, he was eviscerated by Chris Christie for mindlessly repeating, virtually word for word, a rant against Obama which was wholly unresponsive to what Rubio had been asked. The indelible impression was of an Hispanic Ken doll whose tape was stuck on replay -- beyond repetitive red meat, no one could figure out what he stood for. Trump had the Wall; Cruz had the old-time religion; Kasich had decency. Rubio had himself.

And so he flamed out, quickly devolving from the establishment's last hope to a punching bag for Trump. In the process, he tarnished his own brand in a last-ditch change of tactics, indulging in a puerile exchange of insults with Trump so embarrassing as to make one cringe. After which Trump, who at least remained in character, clobbered him in Florida.

Abruptly, Rubio found himself without political property. His Senate term was up -- as a presidential candidate, he had ostentatiously declined to run for reelection, expressing frustration with a senatorial stasis which fueled the self-proclaimed "sense of urgency" compelling him to run for president. Even after dropping out, Rubio insisted that he was done with the Senate: "I've always said like 10,000 times I will be a private citizen in January."

The 10,001st was, apparently, the charm. A few weeks later, Rubio declared for reelection, trampling the hopes of a longtime friend who was running in the GOP primary. To be fair, Mitch McConnell asked him to run so the party could retain his seat; to be real, Rubio needs a base from which to run again in 2020, and even the Senate will do. Either reason will suffice.

So what did Rubio say? That the mass shooting by an ISIS sympathizer at a nightclub in Orlando inspired his change of heart: "I think when [a tragedy] visits your home state, when it impacts the community you know well, it really gives you pause to think a little bit about your service to your country and where you can be most useful to your country."

Please. Still, in the face of such sentiments, it seems churlish to dwell on Rubio's craven allegiance to the NRA, and his implacable opposition to any gun safety measures -- including barring sales to those on the terrorist watch list.

In any event, once more Rubio is dipping his toe in presidential waters with his signature caution. To enhance his hope of reelection, he now endorses Trump; to avoid the taint of attending Trump's convention, he split the difference, reminding delegates of his existence by appearing on a giant screen, an ersatz Wizard of Oz.

But to what end? By themselves, the Chamber of Commerce and donor class cannot make him the nominee. Nor can foreign policy hawks. No doubt he will try to reconstitute himself as the face of the post-Trump GOP, carefully contriving a program to blur its contradictions. But the Tea Partiers and evangelicals demand men made of sterner stuff, and Trump's blue-collar base will never make the erstwhile Little Marco the new voice of their outrage.

That is the hell of the GOP's ferocious fratricide. Rubio could not navigate these cross-currents as the fresh new face of 2016. He is no longer fresh; should Trump lose, he will be dead in 2020, a nowhere man going nowhere. Better not to run.

Then there is the man who chose not to run, Paul Ryan.

Nor should he have. Ryan had already given at the office by taking up the thankless role of Speaker. His reward was to have the Tea Party crowd nipping at his heels, hamstringing any hope of passing a budget which, to the extent possible, honored his conservative priorities. And his attempts to thread the needle between supporting Trump and simple dignity were painful to watch. All of which, in turn, exemplifies the problems for Ryan in 2020.

Four more years as speaker will only aggravate the tensions between the hard right of the GOP -- which prefers shutting down the government to compromising their agenda -- and the pro-business crowd, supporters of Ryan, who believe that stable governance will best advance their interests. These attitudes cannot be reconciled: no matter what he does, Ryan will disappoint some in his caucus, and alienate others.

But intramural warfare is but the beginning of Ryan's difficulties. Regardless of how Ryan navigates this divide, should Trump lose Ryan's restive troops will be dedicated to thwarting Hillary Clinton. And so, among the broader electorate, Ryan will become the face of gridlock even as, among angry voters hungry for change, he will become the face of Washington. In this era of distemper, such is the price of actual responsibility.

As for substance here, too, Ryan has a real problem. Ryan has long been the preeminent face of conservative economic ideology, including tax cuts for the wealthy and drastic reform of entitlement programs. But in a time of income inequality and economic insecurity, this agenda has not worn well.

In 2016, it was pretty much rejected by Trump's working-class base. In a general election, one can easily imagine the Democrats portraying Ryan as the weapon of the wealthy in their war against ordinary people. And for those who actually care about a balanced budget, the so-called Ryan budget has never added up.

No doubt Ryan will try to ameliorate these difficulties by soft-peddling entitlement reform and throwing in tax proposals to benefit the middle-class. But he will not easily escape his past support for privatizing Social Security. And while his advocacy of using free market solutions to fight poverty, drawn from his mentor Jack Kemp, will be attractive to moderates, this has little traction among hard-line conservatives. Too many Republicans, as Kemp once privately conceded to a friend of mine, "hate poor people."

Minorities, too. Historically, Ryan has been friendly to immigration reform. And among his more attractive moments of 2016 were his denunciation of Trump's slurs against Mexicans and Muslims. But this runs counter to the essence of Trump's appeal among the Republican base. Here, Ryan is a victim of the GOP's larger dilemma: the conflict between demographic outreach necessary in a general election, and the hard line which works in party primaries -- a hard line which people like Ted Cruz are sure to embrace.

No doubt the party establishment will be looking for a strong conservative who seems more responsible and inclusive. That's Ryan. But within the party at large that will leave him caught between Tea party purists and angry Trump voters.

Beyond that, there are serious questions about whether Ryanomics can sell in a general election, not to mention the evangelical social agenda which Ryan will have to embrace. As respected as Ryan may be among Republican officeholders, his path to the White House is littered with landmines.

Which, with whatever reluctance, brings us to Tom Cotton.

Who? I can hear you asking. A 39-year-old freshman senator from Arkansas who wants you to make him president. Which, more likely than not, will make you nostalgic for your blissful time of ignorance.

Here's Cotton in a nutshell. A hardliner on immigration reform. An implacable foe of criminal justice reform. A super hawk. A favorite of right-wing Zionists and evangelicals. An opponent of equal pay for women and the Violence Against Women Act. A writer for Salon offers this summary of his charms: "Ted Cruz with a war record, Sarah Palin with a Harvard degree, Chris Christie with a southern accent."

So why must you give him any thought? Because this describes the beau ideal of folks who listen to Rush Limbaugh. In other words, a large chunk of Republican primary voters.

Cotton's entrée to politics is admirable in itself -- service as an army officer in Afghanistan and Iraq which earned him a Bronze Star. Regrettably, he also exemplifies the delusion that such an experience, in itself, qualifies one to define the essence of patriotism, meddle in geopolitics and rise to commander-in-chief.

He first came to the attention of conservatives while still in Iraq. After the New York Times published an article about how the U.S. tracked terrorist financing, Cotton wrote a scathing letter suggesting that the authors should be imprisoned. Whatever his intentions, he became an instant darling in right-wing circles.

Writing politically charged letters, it transpires, is something of a specialty. In 2015, Cotton undercut President Obama in our nuclear negotiations with Iran by writing a open letter to the ayatollahs, warning that a Republican president would reject any deal. Though this arguably violated a law barring unauthorized negotiations with foreign governments, 46 Republican senators signed on. Cotton's self-serving showboating helped mark the moment when the GOP reduced the complex question of how best to restrain Iran to just another political wedge issue.

But then reducing complexity to a cartoon is another Cotton specialty. Our nuclear deal with Iran is like the "appeasement of Nazi Germany." Despite the tension between the ayatollahs and Iranian reformists, "there are nothing but hardliners in Tehran." Hezbollah is collaborating with criminal cartels in Mexico "to cross our borders and attack us here." Food stamp recipients are "addicts." Guantánamo has "too many empty beds." And so on.

In this, he is Ted Cruz's equally evil twin -- a smart and educated man who panders to fear and ignorance. But he is playing his Trump card a bit differently.

Unlike Cruz, he endorsed Trump prior to the convention and, not so coincidentally, expressed his willingness to be The Donald's running mate. And he has begun toying with how to propitiate working-class Americans by offering tax relief.

Still, he has been the most blatant of 2020 hopefuls in anticipating Trump's demise. His convention schedule was packed with speeches to delegates from key primary states. And he is favoring those states with the earliest of early visits -- as in, right now.

Should Trump go down, in 2020 Cruz and Cotton will be fighting with Pence over the GOP hard right. If anything distinguishes them, it is Cotton's passion for military intervention as opposed to Cruz's disdain for nation building or Wilsonian idealism. But this suggests why their cage match could be lethal to them both -- even should one prevail, their positions may well prove toxic in a general election. Which might make Cotton Paul Ryan's best friend.

Or better, John Kasich's. His prospective candidacy is the best -- perhaps the only -- test of whether the GOP can adapt anytime soon.

In one sense, Kasich is already unique -- he is the only Republican who retains a chance of stopping Trump in 2016. By virtue of his influence and organization as governor of Ohio, Kasich has something to say about whether Trump can carry the state, without which he is pretty much doomed. Though polling suggests that Trump is ahead in Ohio, it is not hard to imagine how Kasich wants this to go -- revenge, as they say, is a dish best tasted cold.

The larger question is what a Trump defeat would do to Kasich. Unlike Cruz, his opposition to Trump was steady, consistent and dignified. Throughout the primary contest, he rejected Trump in tone and substance. He declined to endorse him without making a show, and stayed away from the convention instead of trampling on Trump's moment. He seems more likely than Cruz to be forgiven, at least by those attracted to principle.

Moreover, Kasich is a staunch conservative -- only in a party which harbors Ted Cruz and Tom Cotton could he be taken for anything else. But unlike either of them, as a general election candidate in 2020 Kasich would possess some real strengths. Just as he was in 2016, in 2020 Kasich is the Republican most likely to beat Hillary Clinton.

He is a son of the working class who looks and sounds like one. He speaks out for decency and compromise in politics. He is an advocate of free trade who, nonetheless, is sensitive to struggling white and blue collar workers. He believes that the GOP needs "an inclusive reform agenda." Once this election is over, he says, "Republicans are going to have to... think about what our party is going to mean to people in the 21st century. If we miss that opportunity, it'll be a big mistake."

But that's the problem -- how many Republicans are willing to accept his invitation?

By the evidence of this year, not enough. Trump is an avatar of anger, not civility; so, for that matter, is Cruz, his closest competitor during the primaries. And Trump's defeat would not only tarnish Pence but summon that siren song of the Republican right -- we lost because we were not conservative enough. This sentiment does not serve Kasich well. Or, for that matter, the GOP as a whole.

2020 is far away. Perhaps Trump will beat the odds and win. Perhaps some series of mischances will leave a President Clinton vulnerable to defeat. But the Republican Party seems built to lose the presidential contests of the future, a fractious coalition of slow learners. And so, perhaps, the only thing which can change this is the ultimate hard lesson -- losing yet again.