It’s a given now that Mitt Romney performed brilliantly in the first presidential debate, but some less-than-obvious benefits are still emerging. Beyond predictable poll bounces and fund-raising jumps, an added gain is the dilemma Team Obama faces in trying to regroup after the shellacking.

Desperately trying to change the storyline, all the president’s men immediately went into DEFCON attack mode. On the stump and in ads, they charged out of Denver calling Romney a liar and promised that a more combative president would show up the next time.

It was a reaction designed to calm Obama’s left-wing base, which was spittin’ mad after his pathetic performance. But the leftward lurch carries a potentially high price.

Obama’s effort to placate the MSNBC crowd clashes with his need to attract moderate independents who will decide the election. It’s difficult to do both at the same time and Obama’s decision to go ultra-negative and nasty creates another opportunity for Romney in the swing states.

It is Politics 101 that candidates shore up their bases in the primary seasons, then move to the center to broaden their appeal for the general election. Romney and Obama both tried to do it at the debate, but with very different results.

Early on, for example, the president tried to cast himself as a reasonable man. It was an echo of the uniter role Obama promised four years ago but rarely kept after he got into the White House.

But just as Romney touted his work with Democrats in Massachusetts, Obama talked of bipartisanship and praised the Simpson-Bowles deficit reduction plan he had shunned. Instead of using “Republicans” as a pejorative, he mentioned them only in the context of issues supported by both parties.

The president’s weak effort was quickly overshadowed by his tongue-tied stupor, and the fury on the left is scrambling the feint to the center. It’s a problem he didn’t expect to face so late in the campaign. After all, he spent two years pandering to environmentalists, unions, young and minority voters. He figured he had them in the bag.

More pandering now to make sure they vote, especially by ramping up slash-and-burn attacks on Romney, are not likely to woo those independents who weren’t wooed already. Attacks that re-excite his base may turn off moderates and drive them into Romney’s camp.

The contradictory challenge Obama faces stands in contrast to Romney’s double success. He managed to touch all the conservative erogenous zones while, in the same 90 minutes, present himself to independents as a sensible, pragmatic alternative to the president.

Consider that conservatives who never warmed to Romney were calling his performance the best by a GOP nominee in decades.

At the same time, a CBS poll of independent voters found that 46 percent believe he won the debate, with only 22 percent thinking Obama did.

Part of the winning approach that deserves more attention was Romney’s defense against the charge that his plan to cut income-tax rates by 20 percent would drive up the deficit or lead to tax hikes on middle-income Americans.

Romney, who previously insisted his plan would be “revenue neutral” because he would eliminate tax deductions, suddenly made three clear promises that left Obama stumped.

In quick order, Romney promised he wouldn’t cut any taxes that added a penny to the deficit. He also said he would not raise taxes on the middle class no matter what and promised that upper-income families would not see their share of taxes fall.

The combined details add meat to his plan for growth and also make cutting the deficit more important than tax cuts. As such, the formulation undercut Obama’s charge that the “math” of Romney’s plan doesn’t work and would penalize the middle class.

Obama’s furious response after the debate, that Romney’s new tax details somehow make him a liar, is crude and reinforces the image of Obama as unpresidential. The charge is also not likely to succeed. The longer the president sticks with it, the better Romney will look to independents.

To continue reading Michael Goodwin's column in the New York Post on other topics, including the Romney vs. Obama plastic cup poll in East Hampton, click here.