South Carolina Senator Lindsey Graham is not very happy with one of his Republican colleagues. During the course of an interview with the Weekly Standard’s Stephen Hayes published today in which he floated the possibility of running for president, Graham dismissed the possibility that Florida’s Marco Rubio should also be considered for the Republican nomination. It’s hard to tell if he’s serious about 2016 but his criticism of Rubio, who, as Hayes pointed out, is at least as strong a voice on foreign policy as Graham, deserves a thorough examination.

The possibility of a Rubio candidacy came up in this context because if the Republican Party were really turning back to its roots as a bulwark of support for national security and away from the isolationist wing led by Senator Rand Paul, then Rubio would appear to be one of the obvious choices as leader. While Graham and his pal Senator John McCain have been the loudest voices on behalf of interventionist policies, no one in the Senate has been as eloquent on the need for a coherent and strong U.S. foreign policy than Rubio.

But while McCain praised Rubio Graham gave his younger colleague the back of his hand in his conversation with Hayes:

I asked Graham about Rubio. Hasn’t he been making many of the arguments you’d be likely to make? Graham wasn’t impressed. “He’s a good guy, but after doing immigration with him—we don’t need another young guy not quite ready,” said Graham. “He’s no Obama by any means, but he’s so afraid of the right, and I’ve let that go.”

Graham’s problem with Rubio stems from the fact that after joining the bipartisan group backing a comprehensive immigration reform bill in 2013, Rubio eventually backed away from the legislation once it stalled in the House. While McCain, Graham and the other members of the bipartisan gang of eight that championed the reform package have stuck to their plan, Rubio now says that conservatives who demanded that the border security portion of the bill be done first before any changes in the immigration system — especially the effort to legalize illegal immigrants and/or grant them a path to citizenship — should be implemented.

For Graham, who is being pushed to think about running for president by his friend McCain, this shift by Rubio shows he doesn’t have the right stuff.

Graham is right to note that Rubio hasn’t always looked like a future president in the past two years. While, as McCain notes, his record on foreign policy has been “very impressive,” there have been moments when he looked uncertain and a bit too interested in tagging along with Republican elements who don’t share his views. The beating he took from the party’s hardliners on immigration did take a toll. But Graham is wrong to castigate Rubio for rethinking his stand on the reform bill. If anything, his willingness to react to events and draw conclusions from them rather than doggedly stick to an ideological position that had been mistaken is a sign of maturity, not inexperience.

The surge of illegals over the border in Texas this year showed that rather than fixing the immigration system, the talk of granting illegals a path to citizenship without first securing the border had created a new incentive for people to cross the border. Moreover President Obama’s threats, renewed last night, to act unilaterally to trash the rule of law and legalize illegals shows that this administration can’t be trusted to enforce any immigration law passed by Congress.

By adjusting his position, Rubio opened himself up to charges of being a flip-flopper and abandoning his positions in order to curry favor with conservatives. But in doing so, he also demonstrated an ability to address difficult issues soberly and in a manner that enables him to make decisions based on reality rather than an ideological position. That’s pretty much the opposite of the pattern demonstrated by Barack Obama, that Graham rightly disdains.

Graham’s chances of winning the Republican nomination are virtually non-existent. While he’s part of the GOP mainstream on foreign policy, no one who has spent so much time offending the party’s base is going to be its standard bearer in 2016. By contrast, though Rubio made a lot of enemies because of his immigration stand, as a former Tea Party insurgent, he has a lot better chance of reconciling with the conservative base than Graham.

But what’s really interesting about this discussion is that while earlier in the year it looked as if the GOP presidential field would not have any strong entries that championed a strong foreign policy, now the roster of potential candidates representing that point of view seems to be getting crowded. Potential symbolic candidacies like those of Rep. Peter King and former UN Ambassador John Bolton may be joined by Rubio and Graham as well as Senator Ted Cruz and Rick Santorum, both of whom also share many of the views espoused by McCain and other GOP hawks.

Graham’s carping about Rubio notwithstanding, the real news here is that as the isolationist moment in American politics ends, the GOP’s natural leaders on foreign policy are reasserting themselves.