Another tough ad is out Tuesday attacking former House speaker Newt Gingrich on a laundry list of issues.

Restore Our Future, a super PAC that backs former Massachusetts governor Mitt Romney, released the ad, which is called “Happy” and is airing in Iowa.

“You know what makes Barack Obama happy?” the narrator asks. “Newt Gingrich’s baggage. Newt has more baggage than the airlines.”

The ad hits Gingrich’s work for Freddie Mac, his 1997 ethics reprimand, and his co-sponsorship of legislation with Rep. Nancy Pelosi (D-Calif.) — including the fact that the United Nations Population Fund, which anti-abortion advocates criticize as supporting China’s one-child policy, got funding in the same bill.

The ad ends with a long quote from a recent National Review editorial, in which the magazine’s board declared that Gingrich’s “weakness for half-baked (and not especially conservative) ideas — made him a poor Speaker of the House.”

This spot echoes an earlier Restore Our Future spot that declared, “Newt has a ton of baggage.”

Clearly, Romney’s supporters have no intention of letting up before the Jan. 3 Iowa caucuses. Romney Tuesday morning said that loosened limits on outside groups are making a “mockery” of the campaign season. But he has not asked the super PAC to stop airing the anti-Gingrich spots.

Gingrich was on the defensive Monday, acknowledging that a flood of ads attacking his record had hurt his standing in the state.

“Watch TV here for two days,” he said on a stop in Davenport. “Well you get enough negative ads before you start answering them, your numbers go down for a while.”

For months, Gingrich aired no ads in Iowa or anywhere else. Now he and a pro-Gingrich super PAC are starting to fight back.

A Washington Post-ABC News Poll released Tuesday found that nationally, Gingrich and Romney are tied.