Rick Santorum formally “suspended” his campaign last night and endorsed Rubio, saying that he wanted “to find a candidate that really espoused the values” that he believed in:

“He’s a tremendously gifted young man,” he said of the Florida senator. “I just feel a lot of confidence that he is the new generation and someone that can bring this country together.”

The endorsement won’t help Rubio in next week’s New Hampshire primary, since Santorum has extremely high unfavorability numbers in the state and his support there was virtually non-existent. If anything, being linked with Santorum is more likely to cost Rubio support next week. It is nonetheless a notable and revealing choice for Santorum that merits a few comments. I summed it up this way on Twitter last night:

Santorum posed as champion of working-class voters’ interests & reducing immigration, so naturally he sides with pro-amnesty donor favorite

— Daniel Larison (@DanielLarison) February 4, 2016

At least since his first presidential campaign, Santorum has been presenting himself as the voice of working-class voters and arguing that the GOP has neglected them too long. In connection with that, he adopted some of the most restrictionist positions on immigration in the 2012 and 2016 fields. He played at being a quasi-populist in opposition to Romney, and in the years following the 2012 election continued to argue against the mentality in the party that celebrated business owners and no one else. By endorsing Rubio, he made it plain that all of that takes a backseat to supporting an aggressive foreign policy.

Though the endorsement doesn’t matter that much in itself, it is representative of Santorum’s priorities and the distorting effect that super-hawkish foreign policy has on the GOP as a whole. Faced with a choice between candidates that have at least some credibility with conservatives on immigration and those that have none, Santorum chose one of the latter. When choosing between candidate that already gets a lot of their support from working-class voters and one that is the clear favorite of the donor class, Santorum chose the latter. It isn’t an accident that Santorum also happened to back the most hawkish candidate still running, since the former senator has repeatedly shown that it is hard-line foreign policy that matters more to him than anything else.

It’s true that Rubio and Santorum are both socially conservative, but Rubio is not the only credible social conservative left in the race. But the thing they have in common that distinguishes Rubio from his main competition is that he is by far the most vocal and aggressive hawk left. If Santorum and Graham had never run, that would have been true from the start. I’m sure Santorum can’t abide Trump for all sorts of reasons, but his main complaint against Cruz is on foreign policy. Ever since Cruz used “neocon” in a pejorative way last year, Santorum has been attacking Cruz and saying that his use of that word proves that he isn’t a “Reagan national security conservative.” In light of that, it was practically guaranteed that he would end up siding with Rubio. Santorum is confident that Rubio is just as ideological and dangerous on foreign policy as he is, and he has every reason to be.