Rubio’s big idea is that nominating him will send a message to America that the Republican Party is fully prepared to embrace and lead diversifying America — in short, that it is not captive to the xenophobic forces and hostility towards demographic and cultural change that Trump has unleashed and embodies. Rubio’s “children of the Reagan Revolution” line suggests he hopes to remake the GOP in the eyes of voters who were born during the Reagan years (35 and under) or politically came of age during those years (people who are in their 40s, as Rubio is). The photo ops with Haley seem designed to portray a GOP that is more comforting to cosmopolitan and suburban swing voters.

It is true that if Rubio were nominated, he’d probably be better positioned than any other GOP candidate to make a good pitch to young voters, Latinos, and suburbanites. But consider what Rubio has had to do, in substantive terms, to get even to this point. If anything, Rubio is not the candidate who confronted Trump’s xenophobia most forcefully. The candidate who was most willing to mount a sustained moral argument against Trumpism — Jeb Bush — is now gone from the race.

Rubio has arguably done as much to surrender to the terms of the debate that Trump has laid down as he has to challenge them. He has shrouded his past support for legalization of the 11 million in clouds of vagueness about the need to secure the border first. He has now echoed Ted Cruz’s hard-line vow to end Obama’s executive action protecting DREAMers — many of whom have spent most of their lives in America — from deportation. He has on occasion tip toed around Trump’s most wretched anti-Muslim demagoguery. More broadly, as Jonathan Cohn argues, Rubio is not at all moderate on a number of other issues; arguably there is no candidate left who actually represents the party’s moderate voters.