Still, the Right to Rise onslaught is a decent explanation for Rubio’s stagnation. But not a complete one, since it’s not as though Jeb actually controls the entire Republican establishment. If his donors were really unhappy with his strategy they could desert en masse to Rubio; if leading Republican politicians felt certain Rubio was the better bet, they could counter Jeb’s ads with a wave of endorsements. But they haven’t, again despite Rubio’s higher favorables and better general election odds. Which raises the possibility that …

Rubio’s a little too conservative. Both the Republican donor class and the New Hampshire electorate, in slightly different ways, are more moderate or even liberal than the wider Republican electorate. Meanwhile, as Harry Enten of FiveThirtyEight points out, Rubio is a lot more conservative than his “great establishment hope” image currently suggests.

Moreover, his conservatism is most pronounced on social issues, which makes him culturally alien to both the libertarian and Yankee moderates of New Hampshire and the secular and socially liberal segment of the party’s donor base.

Which is why it isn’t necessarily surprising that Rubio is polling slightly better in evangelical-heavy Iowa than in New Hampshire, or that he’s having trouble putting away more moderate figures like Christie and Kasich in the latter state. It may well be, as Enten suggests, that a lot of Republican bigwigs are just much more politically and culturally comfortable with the other candidates in the establishment “lane,” and so they aren’t ready to throw in with Rubio’s piety and Tea Party-ish voting record until they have no other choice.

Then there also might be a more personal element as well …

Rubio seems a little too ambitious. He’s no Ted Cruz, whose naked self-promotion and penchant for making enemies has left him effectively running against the entire institutional party. But as Matt Yglesias of Vox notes, Rubio’s ascent has been marked by repeated acts of rebellion and opportunism — many of them successful, all of them quite normal for politicians, but condensed into a relatively narrow span of time.

The G.O.P.’s history as a royalist party is somewhat exaggerated, but it has repeatedly handed nominations to elder statesmen in years when it seems to be their turn, and the royalist tendency is naturally strongest in the party elite. It may not be only Jeb Bush’s inner circle that regards Rubio’s rise as a little swift, and his decision to run as a little premature, even arrogant. There may be a sense that he needs to prove himself with voters, to actually win a caucus or a primary, before he can lay claim to wide support.