As Sean Sullivan and I noted this afternoon, Sen. John McCain (R-Ariz.) has undergone a pretty significant political evolution over the past decade on the issue of illegal immigration.

But while he may be the best example of the GOP's uncertainty on the issue, he's hardly the only Republican/conservative to shift positions/emphases over the course of his career.

A sampling of some of the more notable recent converts:

* Sen. Marco Rubio (R-Fla.), who is heading up the effort today, said in March 2009 during the early stages of his primary campaign with then-Gov. Charlie Crist (R) that he would never support an approach that legalized current illegal immigrants.

"No. 1, it demoralizes the people that are going through the legal process," he said at the time. "It's a very clear signal that why go through the legal process if you can accomplish the same thing through the illegal process? And No. 2, it demoralizes the people enforcing the law. So I am not and I will never support — never have and never will support — any effort to grant blanket legalization amnesty to folks who have entered or stayed in this country illegally."

* Rep. Steve King (R-Iowa), a staunch conservative and illegal immigration hawk who is weighing a Senate bid, said Monday that he agrees "with most of the language in the very broad guidelines" of the Senate proposal. You don't have to look far, though, to see where he has differed from that kind of approach.

Rep. Steve King (R-Iowa). (Alex Brandon/Associated Press)

Just after the November election, King saw his party drifting toward comprehensive reform and remained adamantly against such an approach: "We will see ‘open borders’ Republicans team up with Democrats to try to do some things to resolve what they call ‘comprehensive immigration reform.' We know that that always includes a component of amnesty, so we’ll be back to discussing this again about the rule of law, and I’ll be fighting to defend the rule of law.”

* House Speaker John Boehner (R-Ohio) is now open to guiding comprehensive immigration reform through the House. But in 2010, he told the Pittsburgh Tribune-Review that border security needed to be done first and that illegal immigrants needed to return to their home country if they wanted citizenship: "If people want to become citizens, they need to do it the right way. Go home, sign up, get in line like everybody else.”

(Side note: Another politician who has shifted positions — and acknowledged doing so — is Democratic Senate Majority Leader Harry Reid, who in 2006 apologized for authoring a harsh crackdown on illegal immigrants more than a decade earlier.)

The movement is not limited to GOP politicians, though. Perhaps the most significant and broadest shift has been in the class of conservative commentators.

* Sean Hannity said after the November election: "We've got to get rid of the immigration issue altogether. It’s simple to me to fix it. I think you control the border first. You create a pathway for those people that are here. You don’t say you’ve got to go home. And that is a position that I’ve evolved on. Because, you know what, it’s got to be resolved."

* Around the same time, columnist Charles Krauthammer said much the same thing: "I’ve always been of the 'enforcement first' school, with the subsequent promise of legalization. I still think it’s the better policy. But many Hispanics fear that there will be nothing beyond enforcement. So, promise amnesty right up front. Secure the border with guaranteed legalization to follow on the day the four border-state governors affirm that illegal immigration has slowed to a trickle."

* Mark Levin has been more hesitant. He said around the same time that the GOP's move toward immigration reform amounted to "race pandering" and that the party had “surrendered to the left’s arguments and their agenda.” But after interviewing Rubio last week, he sounded moved: "This is very fascinating to me,” he said. "I still have a number of questions, but that’s for another day."

* Rush Limbaugh took a similar tack Tuesday, toning down his strident criticism of comprehensive reform during an interview with Rubio. "You're meeting everybody honestly, forthrightly. You’re meeting everyone halfway," Limbaugh told Rubio. But then he added: "Obama is seeking political victory. Obama doesn’t care about enforcing existing law, so people say, why would he enforce anything new?"

* Hugh Hewitt, who opposed the 2007 comprehensive bill, said in a recent column that people should follow Rubio's lead. "Marco Rubio has credibility and the gift to cut through the noise and get regularization done. Listen to him. Do what he says. It isn't that complicated."

The fact that these conservative talkers have changed their tunes is perhaps the biggest development of all. The fact is that Republicans in Congress fear what people like Limbaugh, Levin and Hewitt will say about them if they approve a path to citizenship.

If they know those guys will give them political cover for their votes, it makes it a heckuva lot easier to make the leap — a big reason why Rubio is investing so much time in reaching out to them.

"Any change in tone among talk radio/conservative TV personalities is very significant in my opinion," said Luke Frans, executive director of the GOP polling consortium Resurgent Republic. "That's what floods GOP offices with constituent messages. But at the end of the day, good policy leads to good politics."

This entire debate is in its infancy. But if people like these commentators and King are on-board, it's hard to see how some kind of comprehensive reform doesn't get done.