GOP presidential candidate Newt Gingrich is set to officially exit the race Wednesday in Arlington, Va. and is telling USA TODAY that he'll soon endorse Mitt Romney. But can the former speaker make voters forget the millions of dollars worth of attack ads that he and the super PAC supporting him launched against the man Gingrich now says will be the next president?

We have compiled a highlight — or should we call it lowlight? — reel of the ads that ran in early primary states when Gingrich was Romney's main rival. It underscores how the intense negativity of this year's primary campaign, fueled largely by the big-spending third party groups that have arisen in the wake of the Supreme Court's Citizens United ruling, has complicated the traditional efforts to mend fences at the end of a nomination fight. The ads were placed by either the Gingrich campaign or by Winning Our Future, a well-funded super PAC run by former Gingrich staffers that supported his candidacy.

Winning Our Future spent about $3.7 million on attack ads against Mitt Romney back when Gingrich was Romney's main contender in January, an analysis using Sunlight's Follow the Unlimited Money tracker shows. The money went for TV, radio, Internet and email ad buys, mostly in Florida and South Carolina.

Gingrich's own campaign committee spent about $900,000 on negative advertising, according calculations by the Washington Post using findings from the ad-tracking company Kantar Media CMAG. The specific amount used to target Romney is not disclosed, but the ads that take aim at him can be viewed here (and here and here and here). 

Some of those ads include biting critiques about Romney's electability. They called him a faux-conservative who governed in favor of abortion rights, would not be a strong defender of gun rights, and who can't beat President Obama, whose reelection Gingrich says "would be a genuine disaster," in a farewell video to supporters that he released Tuesday. Winning Our Future sharply criticized Romney's record at the private equity firm Bain Capital, hammering him for overseeing a company in the early 90's later fined for Medicare fraud and producing a documentary that portrayed Romney as a corporate raider. 

While Winning Our Future has made no effort to sanitize the record on Romney, Gingrich's official campaign committee recently has tried to hide its attack ads, making them private on its YouTube account. Gingrich spokesman R.C. Hammond has not returned an email asking why. However, a YouTube user named NewtonGingrich has preserved the negative ads. 

The pro-Romney super PAC Restore Our Future scrubbed its YouTube account of ads bashing another Romney rival for the presidential nomination, former Sen. Rick Santorum, some time after he dropped out of the race on April 10. Then, in the final days of April, after Gingrich said he would exit the race, the super PAC also made its anti-Gingrich ads private. All but two of Restore Our Future's ads are now hidden.