As the debate over immigration reform unfolds, Rubio has become the lynchpin for its success. He is the only member of the Senate’s bipartisan working group on immigration who is beloved by most conservatives. He is the rare Republican who can participate in a Senate “gang” and still be cheered by a bevy of right-wing commentators.

But if these calls are any indication, the first-term Florida senator is aware that his popularity and power are fragile. Conservatives are open to his immigration plan, which would combine tougher border enforcement with new rules for undocumented workers, but they remain generally wary of comprehensive immigration reform.

Rubio’s response to the Right’s entrenched hesitation has been enthusiastic engagement. As he talks to Medved and blogger Ed Morrissey, he shares their skepticism about how such a plan would be implemented. He assures them that he’s simply sharing “principles,” and that the legislation has not been finalized. …

Rubio, however, doesn’t just want to be a conservative darling and quietly wait to be anointed the Republican nominee in a few years. He wants to pass legislation. He doesn’t mind a challenge. He didn’t run for the Senate to merely be a backbencher by day and a Fox News talking head by night.