The strangest aspect of Wednesday night's debate was Mitt Romney's decision to change his tax policies on the fly. Having campaigned hard on a tax proposal that called for $5 trillion in tax cuts, he said flatly that he was not offering a $5 trillion tax cut.

"I don't have a tax cut of the scale that you're talking about," Romney said, even though that is exactly the tax cut he has proposed.

Was Romney for his tax plan before he was against it?

Romney's willingness to remake himself one more time brought into sharp relief a central flaw of his candidacy: Having campaigned as a moderate when he ran for governor of Massachusetts, he veered sharply to the right to win the Republican presidential nomination. Now, with the election just weeks away and polls showing him falling behind in the swing states, he has decided that he needs once again to sound moderate, practical and terribly concerned about the middle class -- and that is the person he sought to be in Denver.

The candidate who has repeatedly attacked regulations was quick to insist: "Regulation is essential. ... You have to have regulations so that you can have an economy work." Romney then reiterated his criticism of the Dodd-Frank Wall Street reform legislation. But this scourge of big government during the primaries took care to let everyone know that he was not about to turn the United States into an Ayn Rand utopia.

Having hidden his Massachusetts health care plan behind "Repeal Obamacare" rhetoric in the primaries, Romney warmly embraced his own plan -- without explaining why repealing a national health care system modeled on his plan would in any way be consistent with his sloganeering against the president's central achievement.

Romney certainly proved his ferocity in Denver, drawing on the persona that had dispatched Newt Gingrich during the primaries. He relentlessly attacked President Obama on the economy, the budget deficit, health care and just about anything else the president has touched. Romney repeatedly used the word "crushed" to describe the impact of the president's policies on Americans' well-being.

"We know that the path we're taking is not working," Romney said late in the debate. "It's time for a new path."

In the early going, Obama seemed reluctant to go on offense and backed away from several opportunities to engage Romney. The president appeared far more interested in explaining than attacking, more concerned with scoring policy points than raising larger questions about his opponent's approach. The words "47 percent" did not come up.

Obama did return repeatedly to a central point: Romney's vagueness in his proposals on taxes and health care. He charged that Romney was hiding the details of those plans because they would prove unpopular with and harmful to the middle class. Several times, using different language, Obama effectively asked: If Romney's ideas were genuinely helpful to average voters, wouldn't he be shouting their particulars from the rooftops? And at several points Obama spoke of the baleful impact that the budget cuts proposed by Rep. Paul Ryan, Romney's running mate, would have on Medicare, student loans and community colleges.

Still, Obama chose not to put Romney on the defensive, instead telling voters what he himself had done and why. Obama was more deferential than Romney was to moderator Jim Lehrer and was more willing to let Lehrer interpret the remarkably loose debate rules.

Only in the last minutes did Obama find a stronger voice in describing his achievements. He contrasted his willingness "to say no to some things" with Romney's refusal to say no to "the more extreme parts of his party."

Romney entered the debate facing a skeptical pundit class and a party faithful that perceived his campaign as floundering. This he reversed on Wednesday. By going on the attack, he won himself strong press notices and shouts of joyous relief from his own camp. Obama, by contrast, surprised many of his supporters by not even repeating criticisms of Romney he has made in his own stump speeches.

But Romney's relentlessness may not play as well with swing voters. His decision to change his tax plan on the fly, rather than to defend it, will provide fodder for further Obama attack lines on how it would affect middle-income voters. And his obvious pivot to a new political persona -- or, perhaps more precisely, his reversion to his older, more moderate self -- will lead to more questions about who the real Mitt Romney is.

(c) 2012, Washington Post Writers Group