Massachusetts Mitt is back. The right-winger of the Republican primaries is gone. Forget everything Mitt Romney has said in the past. In Wednesday night’s debate, he moved from the right to the center, where he needs to be in order to win the presidency.

Unfortunately, President Barack Obama let him get away with it in their debate at the University of Denver. He did challenge Romney on the heart and soul of the Republican candidate’s campaign, a dismantling of the economic and social safety net and a tax plan that would reward the very rich and hurt the middle class, the working poor and the unemployed. But Obama failed to point out the inconsistencies between what Romney was saying in the debate and what he has been saying in his campaign. And the president failed to show outrage at the Romney tax plan. Instead, his manner was annoyingly cool.

The post-debate media analyzers welcomed Romney back to the center, a position they love. His months of attacks on social and economic justice programs and immigrants — necessary to knock out Newt Gingrich, Rick Perry, Rick Santorum and the other primary opponents — will be forgotten. The latest incarnation of Romney will be embraced by the mainstream media. To political journalists, every day is new. There is no past.

There was no better example of a missed opportunity than the way Obama dealt with the Romney tax cut proposal, which would slash taxes for the wealthy and have the effect of raising levies for some of the working class and the poor.

Obama pointed out that the tax cuts will amount to $5 trillion over 10 years, and this, along with Romney’s proposed increases in defense spending, will drain money from education, road and transit construction and a variety of programs that help the poor.

Romney, who was hurt by the revelation of a tape showing him heaping scorn on Americans who don’t pay income taxes, took the debate as a chance to portray himself as a friend of the middle class and now insists he would not reduce the burden on high-income families, as he’s been promising for months. He said he would reduce taxes for all, paying for it by eliminating tax deductions and exemptions. “I am not asking for a $5 trillion cut,” Romney said. “Everything he [Obama] said is wrong.”

Ezra Klein commented in his Washington Post blog during the debate that “Romney has said he’ll close tax breaks to pay for all of it — but he hasn’t named any of those tax breaks. Romney says he deserves credit for the offsets he hasn’t named.”

Obama made that point but not as well. He did not mention that Romney had signed anti-tax crusader Grover Norquist’s no tax pledge earlier in the year in a blatant effort to win Republican right-wing primary votes. And, amazingly, he did not call Romney out on his 47 percent comments, which were a real attack on the middle class.

Obama did show more passion when talking about health care, the major accomplishment of his administration.

Romney skimmed over the fact that he would completely change Medicare, making it a voucher system in which the government would give recipients a certain amount of money they could use to buy insurance policies. It wouldn’t apply to present recipients, he said, or those over 54. If you fit into that age category, you don’t have to listen.

But if you are 54, said Obama, you had better listen. He explained why the vouchers would weaken medical care for seniors. He’s right, but it’s complicated. Obama would have done better to emulate Bill Clinton and speak of Obamacare — a name the president now embraces — with more emotion and empathy for those it will help.

Obama let Romney get away with claiming the United States has the world’s best health system. Hasn’t he or anyone else in his administration heard that in 2000 the World Health Organization ranked the U.S. 37th among health care systems in the world? In 2007, the United States’ rate of almost seven infant deaths per 1,000 live births was worse than the infant mortality rate of 30 other developed nations.

Nor did Obama mention the many other issues that divide him from Romney and the Republican vice presidential nominee, Paul Ryan.

What about abortion and birth control? What about gay marriage, which he now supports? Or immigration, having given thousands of young immigrant men and women a chance to remain in the United States to study and work?

I’m not saying he should have fired off a bunch of smart aleck zingers to feed the media beast. But the president should have boasted of what he has done, not merely defended it. Does it take Bill Clinton to point out that the Obama administration saved the country from a recession?

For the next month, we’ll be deluged with the new Romney, the faux moderate, the media darling. Maybe Obama will do better next time.