The ad will run on a $320,000 buy for a week starting Thursday, and ties Tisei to the Tea Party, a common attack from Democrats in the race.

Tisei has been running a strong campaign, and Republicans believe he could be the one Republican to pick them up a seat in liberal-leaning Massachusetts. His campaign has been aided by the scandal surrounding Tierney's family's gambling ring.

Though the congressman says he knew nothing about it, his wife was sentenced to 30 days in jail for her role in the ring, and Republicans have hammered Tierney on the issue.

The Hill rates this race as "Leans Republican," as those attacks seem to have taken their toll on the incumbent — in a Boston Globe poll out in early October, Tisei led Tierney by 6 percent.

House Majority PAC formerly withdrew funds from the Boston media market in late September, and the Democratic Congressional Campaign Committee scaled back its buy in the area in mid-October. But with this new infusion of funds, Democrats might be hoping to give Tierney a second wind going into the final stretch.

The political action committee also launched new ads in Illinois's 2nd District, against Republican Jason Plummer, and New York's 1st District, against Republican Randy Altschuler.