One immediate benefit of the Obama-Clinton detente is that full attention can now be paid to John McCain's serial wafflings. After all, the "maverick" has been on quite a roll.

Last week, for instance, McCain failed to show up in the Senate for a crucial vote on a bipartisan bill - co-sponsored by his friends and allies John Warner and Joe Lieberman - that was designed to curb the worst effects of climate change. Going AWOL was an interesting choice, considering the fact that, just three weeks previous, McCain had been talking about the importance of this climate change bill ("I hope it will pass, and I hope the entire Congress will join in supporting it and the President of the United States will sign it"); and that, for many months previous, McCain had been trying to woo centrist independent voters by talking up his concerns about global warming (complete with photos of him walking through forests), and generally signaling that his environmental views are far greener than those expressed by President Bush.

Anyway, he didn't show for the green vote that he deemed so important. Which actually was not much of a surprise, because when the Senate brought up an amendment, one year ago, that would have curbed some Big Oil subsidies in order to fund renewable energy, McCain didn't show up for that either.  And last Dec. 13, when the Senate tried to unclog some GOP-imposed parliamentary roadblocks, in order to again shift some Big Oil subsidies to renewable energy, McCain didn't show up for that either.

But his latest global warning bailout wasn't the only highlight last week. He also flip-flopped on the issue of surveillance and unchecked executive power, embracing the conservative position that presidents should be allowed to act in an unfettered fashion.

In an online letter to the conservative National Review, a McCain aide said that the candidate applauds President Bush for wiretapping American citizens without warrants, despite the 1978 federal law that has long required such warrants. According to the letter, McCain believes that working closely with the telecoms on survelliance is "constitutional and appropriate...as authorized by Article II of the Constitution." That's a signal to conservatives that McCain supports the concept of an all-powerful "unitary executive," freed of the normal congressional checks and balances.

Yet that's not what McCain was saying last winter. In a questionnaire, the Boston Globe asked him whether he believed that a president could conduct warrantless domestic surveillance in defiance of federal law. In response, McCain said that such laws don't apply to surveillance conducted abroad, and then said: "I think that presidents have the obligation to obey and enforce laws that are passed by Congress and signed into law by the president, no matter what the situation is...I don't think the president has the right to disobey any law." (Emphases mine.)

So he's dining at the Waffle House over climate change and executive power...anything else? Absolutely:

Three weeks ago, a senior McCain aide told ABC News that the candidate does not intend to alter the absolutist anti-abortion plank in the Republican party platform. The GOP plank has long decreed that abortion should be illegal under all circumstances, even if the woman is pregnant as the result of a rape or an incident of incest, and even if the woman might die during pregnancy. But McCain's hands-off posture is yet another flip-flop, because he had indicated twice in the past - in 2007, and during a 2000 debate with Bush - that the plank should be changed to include exceptions for rape, incest, and the life of the mother.

We've also watched McCain (in a January debate) go AWOL on his own immigration path-to-citizenship reform bill. Until he got too much heat from the GOP conservative base in 2006, he was for it. But when asked in the debate whether he would be willing to vote for his own bill if it resurfaced in the Senate today, he replied: "No, I would not."

This exchange occurred shortly before another flip-flop, this time on torture. McCain had long been on record as opposing the practice of waterboarding as an interrogative technique; yet, in mid-February, he voted against a Senate bill that would have required CIA interrogators to obey the U.S. Army Field manual - which bars waterboarding. (At least he showed up for the vote this time.)

So, what gives with all this waffling? That's an easy one, and it speaks to McCain's chief challenge in this election.

He badly needs to outduel Obama among centrist, independent, swing voters. That's the key to victory. Yet he won't even be able to duel effectively unless he first locks down the conservative voters in the GOP base. The problem is, a lot of those voters have never been enthusiastic about McCain, and thus far there is little evidence that he will mobilize them in the enthused and outsize numbers that helped put Bush over the top in his '04 re-election race - particularly in crucial states such as Ohio.

That's why we're hearing so much double talk. McCain tilts toward the centrists on executive power (presidents should obey the law), then tilts rightward. He makes centrist rhetorical noises on climate change and the environment and torture and abortion, then ensures that he won't actually cast votes or take any action that the right can use against him.

Can he satisfy both potential constituencies? Bay Buchanan, the conservative activist and sister of Pat, doesn't believe it matters what McCain does. As she wrote online the other day, "(I)n reality, there is only one candidate in November. Barack Obama. In November he will win or he will lose. John McCain is relevent only in so far that he is not Barack Obama. The senator from Arizona is incapable of energizing his party, brings no new people to the polls, and has a personality that is best kept under wraps."

Now there's a ringing endorsement.

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By the way, McCain floated an interesting talking point last night. During an interview with NBC's Brian Williams, he said: "Senator Obama says that I'm running for Bush's third term. It seems to me he's running for Jimmy Carter's second."

Clever line, perhaps. McCain needs to beat Obama decisively among the high-turnout senior voters. A voter who is 65 today was 37 during the 1980  election, when Carter tried unsuccessfully to parlay his failed track record (stagflation, long gas lines, Iranian hostage crisis) into a second term. So those grim Carter memories are probably quite accessible.

On the other hand, the GOP tried repeatedly to invoke Carter during Bill Clinton's '92 campaign, to no avail. And consider this: There are tens of millions of Americans today, age 45 or younger, who were not even old enough to vote when Carter sought re-election. Assuming they know or care what McCain was referring to, are they likely to judge Obama in accordance with what happened in 1979?