John McCain denies that Hagel is a Republican:

McCain scoffed at claims that Hagel would be a Republican voice in a mostly Democratic Cabinet, saying to “allege that Hagel is somehow a Republican — that is a hard one to swallow.”

Some of this could be explained by McCain’s bitterness that Hagel didn’t support him in 2008, but this also happens to be representative of a lot of Republicans’ views of Hagel. Because Hagel rejected some of the failed and hard-line policies of more hawkish Republicans, and because he hasn’t been willing to adopt the party line on certain foreign policy issues, the people who helped wreck the party with their awful foreign policy ideas no longer consider him to be one of them. If being a Republican required one to embrace McCain’s preference for reckless and aggressive policies, there would be no incentive for foreign policy realists and skeptics to belong to the party. Fortunately for the Republicans, that isn’t the case, and there is a Republican foreign policy tradition of prudence and restraint waiting to be revived. Unfortunately, some of the people most likely to revive it have been effectively exiled from the party, which has the effect of making things worse in the near term.

Of course, Hagel is a Republican for as long as he is registered that way and wants to claim the label, and he obviously belongs to a tradition of Republican internationalism with which he consciously identifies. The question to ask might be: why would someone like Hagel still want to be associated with the GOP in its current state? As necessary and desirable as reform of Republican foreign policy is, there is a danger that the GOP’s foreign policy maladies will grow worse in response to Hagel’s likely nomination in the near term before they are remedied. Perhaps this is a necessary stage in the cure of these maladies, as Hagel’s nomination could provide the occasion to expose and then discredit the fanaticism of Republican hard-liners.