As John Judis says, it's his biggest problem with the conservative base; indeed, it may be his only big one. Right-wingers aren't going to sit at home in a McCain-Hillary race because of the Gang of 14 or waterboarding or McCain-Feingold, but some of them might just stay home if they think there isn't a dime's worth of difference between the candidates on immigration. With this in mind, John O'Sullivan argues that he needs to take a pledge to never support anything like the comprehensive reform he backed last year; meanwhile, Peter Robinson suggests that he promise to sign an executive order to build fences along the border the day he takes office.
Knowing McCain, the former seems to me unlikely to happen, while the latter pledge doesn't seem like it would go nearly far enough. So if I were advising his campaign, I'd tell him to wait till he has the nomination sewn up - so he can't be accused of pandering to primary voters - and then roll out, as part of a broader domestic-policy agenda, a "comprehensive" (yes, that word) border security proposal, one that not only boosts spending for fence-building, agent-hiring, and new technologies along the U.S.-Mexico line, but swipes a bunch of Fred Thompson's proposals on beefing up interior enforcement as well. And he should pledge, on his honor, to make the plan a top priority for his first one hundred days in office - for instance, by promising not to sign any spending bill that Congress sends him until they deal with border security in the manner he suggests. This is already effectively his message: He's said that the lesson of last year is that voters want enforcement first. But by putting real meat on the bones of that "enforcement first" promise, he can convince at least some conservatives that he really has learned his lesson - while simultaneously leaving the door open, as he seems determined to do, to supporting some sort of earned-legalization program well down the road.
This is, not coincidentally, roughly my own position on immigration - serious enforcement today, some form of amnesty if and when we manage to reduce the rate of illegal entry. But I happen to think it's a winning political message as well, particularly for a candidate trying to manage the difficult feat of simultaneously staying true to his own reputation for principle, placating the Republican base, and winning a general election.
Photo by Flickr user MarcN used under a Creative Commons license.