Heading into the the next Republican debate, if historical patterns hold neither Trump nor Carson will be the nominee.

The Republicans head tonight into their fourth debate. Hopefully this Republican debate will go a little better, seeing as how Fox Business will be eager to stick it to its rival, CNBC, which famously bungled the last one. And this showdown comes just as the race is really clarifying.

Based on the last few weeks of polls, this is a Rubio versus Cruz contest now.

But wait, I hear you say, what about the fact that these aren’t the front-runners in the current polls, where Donald Trump and Ben Carson are neck-and-neck at a little under 25 percent each?

As I’ve explained before, political outsiders are a great vehicle for disgruntled voters to express their discontent early in the primaries, but they never win. Only two kinds of candidates get nominated and elected: those who have previously served in political office, and generals who win major wars.

If historical patterns hold, neither Trump nor Carson will be the nominee.

Of course, trends continue until they don’t, so maybe This Time Is Different. But if we assume the historical pattern will hold, then it is highly unlikely that either Trump or Carson will be the nominee. So that’s the first thing we’re looking for in tonight’s debate: signs of what might cause voters to lose interest in the two main outsider candidates.

The mainstream media has been working overtime to manufacture gaffes to bring Carson down. So far, the attempts have been so lame and obviously biased they have probably helped him more than hurt him. The question is whether he will say anything new that’s embarrassing, or whether the press will find anything real that discredits him.

With Trump, the question isn’t whether he’s made any gaffes or said anything embarrassing. The question is whether any of the things he has already said might actually stick. Or, failing that, we’re looking for signs that Trump isn’t having fun any more, that he will stop being outrageous and start to be boring (which is what everyone seems to be saying about his appearance on “Saturday Night Live,” in which nobody seemed to want to be there, not even him). I suspect that is what would really cut into his support.

So if we assume that something will eventually cause the political outsiders to fade, and we’re only waiting to see what it is, then our attention moves to the candidates with political experience. That is where the race is really clarifying.

Everyone’s poll numbers are flatlining except Rubio and Cruz.

The big thing that has happened since the last debate is that everybody else’s poll numbers are flatlining except those of Marco Rubio and Ted Cruz. Chris Christie and Mike Huckabee got sent back to the kids’ table for this debate. Rand Paul, once at 10 percent in the polls, looks like the next candidate in danger of losing to Moe—that perennial fringe candidate, margin of error. Jeb Bush, who started as the establishment front-runner at nearly 20 percent in the polls, is now at about 5 percent and is mostly just embarrassing himself with undignified attacks on his former protégé, Marco Rubio.

More to the point, all of these candidates are doing what they’ve done all along. Whatever appeal they were going to have to primary voters, they have already had a chance to display. So I don’t think we’re going to see them suddenly perform differently. Their slow fade in the polls is likely to continue.

I’m afraid the same thing probably applies to our last remaining outsider, Carly Fiorina, who has been oddly fading. She does very well during debate appearances, and she may benefit tonight from the smaller number of people on stage tonight. But at this point, she doesn’t need to show us she can shine in a debate. She needs to show she can keep the momentum afterward. If she can’t, she’s not a contender.

The only candidates who have really been gaining since the last go-around are Rubio and Cruz, who have sailed up into the low teens in most of the recent polls. If you assume, as I do, that the nomination is most likely to go to someone who has held political office before, then these are our two candidates.

That’s what might eventually knock aside the outsider candidates. Carson and Trump now can claim a little under half of Republican voters. If everyone else begins to fade to an asterisk and more candidates drop out, then we’ll see Rubio and Cruz dividing the other half of primary voters between them, reaching or surpassing the numbers claimed by the outsiders.

What I’m looking for tonight, then, is a list of reasons to decide between these two contenders.

What we’re looking for tonight is a reason to decide between these two contenders.

The big difference between the two men is pretty clear. Cruz is the more radical and pugnacious, the one who is most likely to promise the conservative base everything it wants and to pick a fight to get it—although there is some question about how effective he has been at doing so, and whether he is more about grandstanding than getting results. But the very thing that makes Cruz attractive to the hard-core conservatives will make him less attractive to moderate swing voters.

So we face an old and unavoidable choice: a candidate who will promise us everything we want but might not make it into office, versus a candidate who promises less but is more likely to be in office to deliver. After seeing what happens when we let a far-left politician control the White House for eight years, we really need someone who is able to get into that office.

Rubio is less radical, but he is more charismatic and likable, with a friendly, natural demeanor. Unlike pundits, bookmakers have their own cash on the line, and they’re giving Rubio by far the best odds of winning. (Although, of course, he will have to struggle to recover from his utterly disastrous Star Wars gaffe.)

When I say Rubio is less radical and more electable, please try to suppress your urge to scream, “Establishment sellout!” He is far more reliable than a lot of the other options we’ve been presented with this year, including his fading mentor Jeb Bush. For those who think foreign policy is an important issue, particularly given the vast mess the next president will have to clean up, Rubio shows a command of the issues and a grasp of the strategic priorities that no other candidate else match. Since this is the president’s first job, that’s a major advantage for him.

If it comes down to Rubio versus Cruz, it’s the best choice we’ve been offered in a long time.

Republican may be in a mood to complain, but if the contest comes down to Rubio versus Cruz, it will be the best choice they have been offered in a long time. That’s what I’m watching for tonight: to help decide which of the two likely options I would prefer, and to savor the fact that two really good candidates just might end up being our choice.

Who knows, maybe we will end up with a brokered convention and a Rubio-Cruz unity ticket that would give every GOP faction something to like. Who could have predicted that?

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