For months and months, movement conservatives and elected Republicans—along with a non-trivial contingent of political commentators and data journalists—promoted as conventional wisdom an idea that was really much more akin to wishful thinking. That idea, boiled down to its essence, was that the very weirdness of the Donald Trump phenomenon—his undisguised bigotry, his total lack of governing experience, the unanimous (if not always vocal) opposition of Republican elites to his candidacy—would sooner or later doom him. 

 When Trump not only didn’t collapse, but built a commanding nationwide polling lead—which he is now converting into a substantial delegate lead—the conventional wisdom took a turn. Once the candidate field dwindled down to a two-or-three person race, the new thinking went, Trump would hit a ceiling. Even if he never exactly collapsed, Marco Rubio and Ted Cruz could slug it out to the GOP convention and conspire to deny Trump the nomination. Alternatively, a single challenger might defeat Trump outright.
In this latter scenario, Trump is assumed to be vulnerable from both directions. In a head-to-head against Cruz, he would succumb to the consolidation of the religious and ideological right, along with a meaningful segment of the Republican mainstream. Alternatively (and preferably, as far as most Republicans are concerned), Rubio would emerge and defeat Trump in the blue and purple states of the Northeast, the Rust Belt, and the West.
For a moment after Rubio’s unexpected (but very narrow) second-place finish in the South Carolina primary Saturday night, you could mistake his shiny mien for a glimmer of hope that Trump’s reckoning was at hand. Or, if not at hand, clearly visible in the middle distance.
But after brief scrutiny, and for several reasons, this second-best fantasy falls apart. First, and most obviously, this is still at best a three-man race between Trump, Rubio, and Cruz. If it never dwindles into a two-man race, then the most Republicans can hope for is a contested convention this summer. After attempting but failing to destroy Cruz’s candidacy a month ago, establishment Republicans are now pressed up against the back edge of their own sword. The Texas senator is in the race, and has no incentive to drop out—especially not before Super Tuesday, when a number of Bible Belt states (and his own) will hold their nominating contests. Trump, it should be noted, just routed the field across almost every GOP demographic, including evangelicals, in South Carolina.
Second, John Kasich is still in the race, too, and has a much more natural appeal than Rubio with the nominally moderate, working-class white voters who will determine the winners of blue- and purple-state primaries in the coming month. Indeed, in states like Ohio, Michigan, and Massachusetts, Kasich is poised to rival or outperform Rubio in the race for second place. But that brings us to the most important point.
The very idea that Trump will encounter resistance outside the South is based on a simplistic and doubly inapt conception of “moderation.” The first premise is that, by promising to appeal outside of the Republican Party’s typical constituencies, Rubio is by definition more moderate than Trump; the second is that appealing to the center in a general election is no different than appealing to “moderate” Republicans in a GOP primary. 
If this race is proving anything, though, it’s that what constitutes “moderation” to elite conservatives (relative dovishness on immigration aimed at swing voters in a general election) isn’t what constitutes moderation among Republican voters (restrictionist immigration policy paired with heterodox support for redistributive social policies). The big flaw in the assumption that Rubio (or anyone, really) can make up ground against Trump in blue states is that “moderate” voters are actually Trump’s ace in the hole.

This appeal very likely extends to nominally moderate Republican voters in the interior West and California, where Republicans will cotton to Trump’s anti-immigration absolutism.
Tuesday night’s Nevada caucus will be an important test of GOP faith. Does Trump have a ceiling? Can Rubio further consolidate the field? Is Cruz’s end beginning? The polling on all of these questions should chasten the right. And in a way, the New Hampshire and South Carolina primaries already revealed how prohibitive Trump’s odds of becoming the GOP nominee have become. Trump lapped the field in a moderate state, and then he did almost as well in a state that should have been fairly hostile to his mix of feigned religiosity, anti-Bushism, and unflinching hawkishness.
If Trump prevails once again, perhaps the conservative establishment will set aside its contrived obsession with whose second- or third-place finish was the most inspiring, and accept that peering past the behemoth in front of them won’t make him disappear.