If you think the right wing of the Republican Party is ready to lie down and accept comprehensive immigration reform without a freakout, Marco Rubio has news for you. Florida's junior senator responded to reports of an impending deal by saying yesterday that he doesn't want to "rush" immigration legislation and called reports of agreement "premature."

By contrast, Rubio's Republican colleague, Lindsey Graham of South Carolina, was practically popping champagne. "I think we've got a deal," Graham told CNN. "There are a few details yet. But conceptually, we have an agreement between business and labor, between ourselves that has to be drafted. It will be rolled out next week."

Graham is not only up for reelection in 2014, his state is less hospitable terrain for pro-immigration sentiment than Rubio's Florida. “If I can sell it in South Carolina, don’t come to me and say it’s hard," Graham said.

So what's the explanation for Rubio's hesitation? One word, or rather number: 2016. Rubio's call to slow down the process on an issue that has been negotiated on both sides of the Capitol for the better part of a decade aligns him -- momentarily -- with the party's all-important conservative base. ("Sessions Slams Leahy for Immigration Rush" reads a recent headline at FoxNews.com, referring to Alabama Republican Jeff Sessions.)

Rubio bravely went on the air in January with talk-radio growlers Rush Limbaugh and Mark Levin, where he made the case for immigration reform. His herky-jerky motions on the issue -- two steps forward, one back -- might be indicative of a cautious nature. It seems more likely, however, that Rubio is simply keeping his options open, and his gaze over his shoulder.

The elites of both parties have concluded immigration reform will go through. The conservative base is the dog that hasn't barked yet. Rubio wants to be sure he doesn't enter 2016 with a set of jaws clamped firmly around his ankle.

(Francis Wilkinson is a member of the Bloomberg View editorial board. Follow him on Twitter.)