Update: On March 13, 2016 I realized I was wrong about this.

When not delighting in the epic meltdown of establishment Republican Party politics, many people I know — my wife, my boss, etc. — are expressing terror at the notion that Donald Trump might actually become president of the United States.

I'm more sanguine. Not out of any particular love for Trump, but because he's actually running on a much less extreme agenda than his "establishment" rival Marco Rubio, who's offering a platform of economic ruin, multiple wars, and an attack on civil liberties that's nearly as vicious as anything Trump has proposed — even while wrapping it in an edgy, anxious, overreaction-prone approach to politics that heavily features big risky bets and huge, unpredictable changes in direction.

Marco Rubio's budget math is ridiculous

Rubio has proposed a tax cut that will reduce federal revenue by $6.8 trillion over 10 years. Numbers that large don't mean anything to people, so for comparison's sake let's say that if we entirely eliminated American military spending over that period we still couldn't quite pay for it.

But of course Rubio doesn't want to eliminate military spending — he wants to spend more. He also promises to avoid any cuts to Social Security and Medicare for people currently at or near retirement. For good measure, he is also proposing a balanced-budget amendment to the Constitution. You could eliminate the entire non-defense discretionary budget and you'd still need $100 billion to $200 billion more per year in cuts to make this work.

This is, of course, totally unworkable. And the process that led Rubio to this point is telling and troubling.

Rubio entered the Senate at a time when an intellectual movement known as "reform" was hot in conservative circles, which argued that Republicans should concentrate less on supply-side tax cuts and more on tax policy focused on the working class. This originally took the form of a $2.4 trillion tax cut plan crafted by Utah Sen. Mike Lee that Rubio signed on to but then kept transforming into a larger and more regressive tax cut, as Rubio came under pressure from the supply-side wing of the party and it became clear that the constituency for "reform" conservatism was limited to a handful of media figures. Eager to prove that his dalliance with the reformocons was over, he actually ended up proposing to entirely eliminate taxes on investment income, meaning that billionaire captains of industry could end up paying nothing at all.

The upshot is a plan that is costly and regressive, yet paired with other commitments around entitlements, military spending, and constitutional amendments that make it completely impossible.

Trump's tax plan is even costlier than Rubio's by most measures. But in his defense, he barely ever talks about it and hasn't compounded the cost problem with a balanced-budget amendment or a firm commitment to enormous quantities of new military spending.

Marco Rubio's foreign policy is dangerous

Rubio's approach to world affairs essentially repeats the "let's have it all and who cares if it adds up" mentality of his fiscal policy. His solution to every problem is to confront some foreign country more aggressively, with no regard to the idea of trade-offs or tensions between goals or limits to how much the United States can bite off at any particular time.

He'd start things off by alienating Latin American allies by undoing the Obama administration's normalization of relations with Cuba in order to return to a decades-long failed policy of isolation.

But that's small potatoes compared with the consequences of Rubio's pledge to cancel the nuclear deal with Iran on day one. He isn't too worried that this will lead to Iran building a nuclear weapon because there will be a "credible threat of military force if Iran decides to ramp up its program." He also wants to deploy more American troops to Syria and Iraq to fight ISIS.

He wants to attack ships and aircraft bound for North Korea that are "suspected of carrying material related to North Korea’s nuclear weapons and ballistic missile programs." He is also hoping to convince China to help with the Korea situation, but his China policy calls for tougher measures to "stand on the side of freedom and human rights, both inside China and on its periphery."

He also wants to send more weapons to Ukraine, increase sanctions on Russia, move more heavy weapons into Eastern Europe, and clarify "that there will be no U.S.-Russia cooperation in the fight against ISIL until Russia brokers the departure of Bashar al-Assad from power."

We really did have a president who tried to govern this way for a year or two. His name was George W. Bush, and starting some time in 2004 he realized it was unworkable. With a larger army already occupying Iraq and a smaller one in Afghanistan, there was no way to make coercive military force the main terms of relating to Iran and North Korea, to say nothing of Russia and China.

Over the next several years, Bush steadily recognized the need to pull back and adopt a more realistic approach to dealing with the world. Not everyone in the Republican Party was happy with this retrenchment, and Rubio is essentially running as the candidate of that faction that wishes Condoleezza Rice never rose in stature to check Dick Cheney's influence and Robert Gates never came in to replace Don Rumsfeld.

In contrast to Rubio, Trump is more prone to offering simply ignorant remarks but also has considerably more restrained instincts. Trump essentially takes the world-conquering nationalism of George W. Bush and turns it inward, offering suspicion of outsiders and a reluctance to launch new wars. This kind of quasi-isolationist thinking isn't exactly my cup of tea, but it certainly reduces the risk of utter catastrophe relative to a return to high Bushism.

Marco Rubio is panicky on civil liberties and immigration

Of course, what has most high-minded liberals alarmed about Donald Trump isn't his tax or foreign policies — it's his bashing of Muslims and immigrants to the United States.

But while Rubio clearly didn't get into the race to push these issues, his response to Trump's rise has been telling and alarming. After the Paris attacks, Trump vowed to shut down mosques where radical preaching might be taking place; Rubio said that didn't go far enough and that a Rubio administration would be willing to stamp out Muslims' freedom of assembly wherever it might present itself. He told Fox News:

It’s not about closing down mosques. It’s about closing down anyplace — whether it’s a cafe, a diner, an internet site — anyplace where radicals are being inspired. The bigger problem we have is our inability to find out where these places are, because we’ve crippled our intelligence programs, both through unauthorized disclosures by a traitor, in Edward Snowden, or by some of the things this president has put in place with the support even of some from my own party to diminish our intelligence capabilities. So whatever facility is being used — it’s not just a mosque — any facility that’s being used to radicalize and inspire attacks against the United States, should be a place that we look at.

Rubio said Trump's proposed ban on Muslim immigration wouldn't pass muster constitutionally but agrees we should block any Syrian refugees from entering the country. Rubio also opposed a bipartisan effort to curb the National Security Agency mass surveillance and promises to permanently extend mass surveillance as president.

Most famously, of course, Rubio was a leading proponent of a bipartisan comprehensive immigration reform bill until it became clear that he'd underestimated the extent of conservative opposition to the idea and began furiously denouncing his own work. Now, Rubio is an enforcement-first guy, who takes such a dim view of both immigration and any concept of limits to the power of the federal government that he wants to cut off all federal funds to towns and cities whose local police departments have chosen to deprioritize immigration enforcement work in favor of crimes that do actual damage to human life and property.

Under pressure from Ted Cruz, Rubio is now promising to start deporting DREAMers as soon as he takes office. He's even turned a wink-nudge promise to bring back torture as an instrument of government policy into an applause line in debates and on the stump.

Nobody knows what lurks in Rubio's heart on these matters, of course. But one could say the same about Trump. What we do know for sure is that Rubio's strategy for beating back the most repugnant aspects of Trumpism is to imitate them.

Marco Rubio is plagued by profound existential doubts

More than any particular policy stance, what is perhaps most troubling about the ebbs and flows of Rubio's positioning is the larger picture they paint of a tendency toward systematic overreaction.

In the wake of Rubio's funny-but-not-serious debate gaffe where he repeated the same canned line several times, McKay Coppins wrote:

But to those who have known him longest, Rubio’s flustered performance Saturday night fit perfectly with an all-too-familiar strain of his personality, one that his handlers and image-makers have labored for years to keep out of public view. Though generally seen as cool-headed and quick on his feet, Rubio is known to friends, allies, and advisers for a kind of incurable anxiousness — and an occasional propensity to panic in moments of crisis, both real and imagined.

I sympathize with this a lot. Two or three days before the launch of Vox.com, I succumbed to my personal occasional propensity to panic and was insisting that we had to delay or cancel the debut of the site. The good news is that more levelheaded voices prevailed.

The even better news is that it is extremely unlikely that I am going to become president of the United States. And I like to think that if the possibility did present itself, my friends, allies, and advisers would have the good sense to politely suggest that a "propensity to panic in moments of crisis, both real and imagined" is not a great quality in a chief executive, and that addressing the substantive concern would be a more valuable contribution to the nation than laboring to keep it from public view.

But so far, playing his hand aggressively has paid off for Rubio. He beat a sitting governor to get into the Senate, and has displaced his own mentor as the favorite of the party establishment. Many of Rubio's moves have looked reckless, but many of them have paid off. And reckless moves that didn't pay off — like the reformocon tax cut or the Gang of Eight immigration bill — haven't killed him either, because he was able to swing hard and fast enough in the other direction to stay alive.

As president, Rubio would likely stick with the approach that's worked for him so far — gambling hard and counting on his ability to swerve sharply if something like launching his presidency by provoking a major international crisis around Iran turns out to create some problems.

If we're all very lucky, it just might work. But I have some concerns.