It would be easier, as some conservatives posit, if Republican votes against the Syria resolution were merely a reflection of their distrust of President Obama. But that simply isn’t so.

Sen. Marco Rubio (R-Fla.) (Joe Raedle/Getty Images Sen. Marco Rubio (R-Fla.) (Joe Raedle/Getty Images

Obama, no doubt, has made it very hard to support military action. His half-heartedness and lack of a cogent policy are evident. But that doesn’t explain the right’s much broader aversion to a forward-leaning foreign policy. A flock of Republicans has come to view isolationism as the new conservative fashion; they recoil when asked to stake out a position of principle in the face of public opinion.

Take Sen. Marco Rubio (R-Fla.). He has long been opposed to military action in Syria. It may be surprising that the use of WMDs has not changed his outlook or focused him on the real issue (Iran), but the more interesting question is why there is a gap between his internationalist rhetoric and his policy prescription when push comes to shove. As one hawkish conservative analyst puts it, Rubio “has always balked at military action. Anyone who knows Rubio well knows he has been weak on this issue all along, despite all his soaring rhetoric about American leadership.”

In explaining his vote, the Florida freshman is quoted as saying:

What’s happening in Syria is a consequence of disengagement. The reason why we don’t have better options in Syria is because we haven’t been more engaged. If two years ago we had made the decision we’re going to find some rebel groups in Syria who are moderate, we’re going to do everything we can to make sure they’re the most capable, effective and organized fighting force on the ground, I’d think that a military strike right now would be a much better option than it is. Because now we don’t know who the beneficiaries of a military strike are going to be but it’s very possible that it could be radical al Qaeda elements who now control significant portions of that country.

None of this makes much sense for no less than five reasons:

1. Worrying about the effect our action will have on al-Qaeda elements is backward. What is certain is that if we don’t act and don’t back non-al-Qaeda terrorists, either jihadists or Bashar al-Assad will benefit.

2. Worrying about a year of failed engagement is beside the point. Because we didn’t act when we had better options is no reason to vote now for no action. This is the if-I- can’t-have-it-my-way-I’m-taking-my-ball-and-going-home mind-set.

3. Like many advocates of doing nothing (including Vladimir Putin and GOP Texas Sen. Ted Cruz and Kentucky Sen. Rand Paul ), Rubio either intentionally or ignorantly exaggerates the al-Qaeda elements, which are only 15 percent or so of the rebels.  Rubio is only putting more delicately absurd comments (Cruz says we are al-Qaeda’s “air force,” while Paul says we would be intervening on al-Qaeda’s behalf) voiced by those who flaunt ignorance.

The Post editorial board has it right:

Both U.S. and independent intelligence estimates show that the 11 jihadist groups identified in Syria make up a small minority of the anti-government forces. U.S. officials say they constitute 15 percent to 25 percent of fighters. Elizabeth O’Bagy, an analyst at the Institute for the Study of War who has travelled extensively inside Syria, reports that al-Qaeda and mainstream rebel forces are largely separated from each other and control different pieces of territory. She says that the jihadists are less interested in defeating Mr. Assad than in establishing a safe haven. . . . An attack that weakened regime forces could, of course, help the jihadists gain ground — but only if the United States and its allies failed to simultaneously bolster the mainstream Free Syrian Army.

4. Rubio, like most opponents of U.S. action, leaves Iran out of the equation. Pro-Israel groups haven’t, and they find Rubio’s willful disregard of the most important aspect of the crisis surprising and deeply disappointing.

5.  Rubio’s complaints about the administration’s past inactivity ring hollow; if he wants to increase American influence, then he should be encouraging bolder action, not tying the president’s hands.

What would cause him to repudiate his own philosophy, make such a weak case for inaction and ignore Iran?

There are two possibilities. Maybe Rubio isn’t as sharp as his defenders claim. It may be that he just doesn’t have the intellectual chops to think through the implications of his own position. That’s possible but unlikely given that he has good advisers around him to walk him through the various scenarios. The other, more likely explanation is that he is nervous about doing more than speechifying on American power. When it comes to actual votes, he prefers to hide in the shadows with the isolationists. He cowers when Heritage Action and his former mentor Jim DeMint rail against U.S. action.  He watches the polls and then reasons backward to devise an excuse for his no vote. Especially after being bashed by the right on immigration, he’s got no stomach to wrestle with the hard right anymore.

Rubio is but one example of the new non-interventionist fad, an unwillingness to buck the right-wing clarion call and accompanying abject fear of crossing public opinion expressed in transitory public polling. But American leadership in the world is not a fashion trend; we cannot cloak ourselves in high-minded internationalism only when it is convenient and popular — or for that matter, when we have a fully competent president. Simply put, it takes political courage to tell the public we as Americans have international obligations, and political courage is in short supply these days.

There are, to be blunt, too many Rubios and not enough Tom Cottons. Cotton is the freshman congressman and Senate candidate from Arkansas. His view is simple: A superpower can’t be weary and can’t cater to the fantasy of American disengagement. Elected officials have to rally the public, making the case for U.S. leadership. (This incidentally was precisely what President George W. Bush understood in backing the surge.)

In sum, Republican objection to action against Syria has less to do with Obama and much more to do with political courage and the influence of pseudo-populists who are in favor of all sorts of daft things. We live in a political era in which there are few giants in the Senate or anywhere else. That problem will, unfortunately, not disappear when Obama leaves office. Blaming him for Republican reluctance on Syria is convenient, but it doesn’t explain the collapse of determined internationalism on the right. For that, conservatives have only themselves to blame.