If you had judged the state of the Republican primary one month ago by surveying the elite punditry of the moment, you would’ve come away with the sense that Marco Rubio was a runaway favorite to win the GOP presidential nomination.

This assessment stood in stark contrast to both national and early state polls, none of which showed (or today show) Rubio anywhere close to the lead, and only one of which (New Hampshire) had him holding a tenuous grasp on distant second.

The logic underlying the pro-Rubio analysis, rooted in the perfectly sensible assumption that Rubio’s support will climb as the Republican field winnows, isn’t entirely unfounded. The field of candidates who could plausibly gain significant numbers of endorsements within the party is much more fractured than the field of “insurgent” candidates. If and when the former field shrinks, the thinking goes, Rubio stands to consolidate enough support to find himself in league with Donald Trump and Ted Cruz.

Unless, of course, he doesn’t.

When other candidates have faltered, Trump and Cruz have surged, but Rubio has barely benefited at all. Nationally he enjoys less than 11 percent support, and falling. In Iowa he’s holding steady at 12.5 percent. He’s enjoying a modest climb in New Hampshire along with other candidates, and in South Carolina both he and Cruz are experiencing small surges, but Cruz at a significantly faster clip.

As Dave Weigel noted at The Washington Post, “The ‘establishment lane’ of the party has fought over a shrinking piece of turf.” In order to match or surpass Trump, Rubio must be the second choice of the vast majority of voters whose preferred candidates will soon exit the race.

Instead, the Florida senator, so prized by the commentariat, has been dragged into a nasty spat with New Jersey Governor Chris Christie, who’s threatening to knock Rubio into third place in New Hampshire. Generally speaking, it’s bad news when a candidate who’s been accorded frontrunner status by the press finds himself in a political brawl with the Bridgegate guy, who’s polling in sixth place nationally. The fact that Rubio will ultimately need most Christie backers to defect to him makes the situation all the more precarious. 

Everyone who studies politics closely seems to agree that Rubio has formidable skills. If he were a charismatic Democrat with orthodox liberal views, he’d reflect the rising American electorate, and thus be better positioned than either Bernie Sanders or Martin O’Malley to challenge Hillary Clinton for the Democratic nomination. Yet he can’t seem to convince more than a small fraction of Republican voters that he’s a worthy first choice. And one reason may be that the Republicans, so derisive of the ethnic and gender politics they see everywhere in Democratic campaigns, are driven by something similar.

Many factors contributed to President Obama’s political success, but one of the biggest is that he resembled the political coalition he represented: young, educated, cosmopolitan, and ethnically non-white.

To the extent that anyone in the Republican primary today holds a mirror up to the GOP base—old, cantankerous, nativist, and caucasian—it’s Donald Trump. Which is to say, it’s definitely not Marco Rubio.

Here again, there is an analogy to Democratic politics. As Matthew Yglesias has written for Vox, one of the most striking things about the Democratic primary campaign has been former Maryland Governor O’Malley’s difficulty gaining traction, despite a lengthier record of progressive success than either Clinton or Sanders.

Yglesias attributes O’Malley’s weaknesses to a variety of factors—dull public speaking, Sanders’s more unapologetic leftism, a waning public interest in elevating governors to the presidency. All of these factors surely contribute to O’Malley’s troubles, but the elephant in the room here is the composition of the donkey party. Most generic white male politicians in the Democratic Party aren’t well suited to speak to the experiences of the voters they must court if they want to win the Democratic presidential nomination. As a left-wing insurgent and the most successful female politician in U.S. history, respectively, Sanders and Clinton don’t have this problem. The only way O’Malley could avoid it would be to abandon liberalism and join the Republican Party.

The story there is no different. Trump’s lily-white juggernaut is defined by its whiteness in deeply unsettling ways. Despite being just as young as Rubio, and of Cuban descent as well, Cruz has escaped the Republican identity politics trap by defining himself in contrast to the wing of the party that believes reaching out to Democratic constituencies is the key to the GOP’s future. He rankles the establishment, he doesn’t speak Spanish, he doesn’t pander to immigrants, and he certainly never supported amnesty.

In part because Rubio’s appeal to voters is peppered with hopeful soundbites and gestures to the future, many of the same pundits who consider him a likely nominee have also compared him to Barack Obama. But those qualities, and that hopefulness, are out of step with the resentful identity politics that drive the Republican Party today. Rubio supporters would never use that term, and would first attribute his difficulties to other issues, like his until-recently sluggish campaign schedule. But they’re learning the hard way that identity politics isn’t just a quirk of liberalism—it is a dominant force behind all politics in the Obama era.