Rick Santorum’s lead in the polls, both nationally and in Michigan, seems to be gone. Nationally, at least according to Gallup’s tracking poll, what was at its peak a 10-point Santorum lead has shifted to a 2-point Romney advantage.

While yet another short-term reversal is certainly possible, the better question at this point is whether the ebbing of Santorum’s momentum was predictable. I’d argue: yup. The key indicator that suggested the polling numbers shouldn’t be taken serious was, again, high-profile endorsements, and in this case the puzzling lack of them after Iowa and then again after Santorum’s big wins in Colorado and Michigan.

We often think of these high-profile endorsements as important because they eventually affect voter behavior. That’s sort of true, although not usually in a direct way; very few voters will wait to see who their governor supports in order to make their own decision. Instead, endorsements generally work indirectly, by giving candidates resources, including money and positive publicity. Moreover, high-profile endorsements are generally indications of more broad-based support among party actors.

But endorsements are also bets that a particular candidate will do well (it’s rare for there to be any incentive to back a likely loser), and they’re bets made by people with inside information. Senators, governors and members of the House either know each of the serious presidential candidates personally or, at most, are at just one remove from them. The governors of Michigan and Arizona probably have someone they trust who has worked with Rick Santorum and has strong opinions about him. And what they’re hearing, apparently, isn’t anything good for Santorum. And it’s not just them: The key indicator here is that even those who are publicly complaining about the lack of a solidly conservative candidate just haven’t shown much interest in supporting Santorum.

In some cases, that may well be because many high-profile Republicans are perfectly happy with Mitt Romney but, in an era of Tea Party primaries, are just afraid to say so. But I suspect that another part of this is that elite vetting is at work, and Santorum — for whatever reason — is falling short. And that’s where it gets back to whether the lack of endorsements has predicted Santorum’s national slump. It could be that those who have followed Santorum’s career closely just didn’t think he was national-candidate material. And judging by how Santorum has done after his unexpected surge, whether it’s telling people they shouldn’t want to go send their kids to college or bashing JFK, it’s hard to say that view was wrong.