Republicans are portraying Speaker Nancy Pelosi (D-Calif.) as a boogeywoman in their attempt to win back the House, according to Democratic National Committee Chairman Tim Kaine.

"I have my own theories about why Republicans often like to make the speaker a 'boogeywoman.' And you might divine my theories from the way I phrased that," Kaine told a National Press Club lunch Wednesday.

Republicans made Pelosi and President Barack Obama an issue in Tuesday's special election for former Rep. John Murtha's (D-Pa.) seat. Both were unpopular in the district but Democrat Mark Critz, a former Murtha staffer, prevailed with a comfortable nine-point margin, which Kaine pointed out several times during his remarks.

He also defended Pelosi's tenure in the House.

"She's done a very effective job especially in a Democratic caucus that is extremely broad," he said. "Being a speaker of a very broad caucus in its diversity and its ideological position is a tough job and she's done a good one. I should have given her praise in terms of that special win last night, because, boy I'll tell you, the House Democrats have quite a track record going winning those special elections. She gets a lot of credit."

Republicans also have made the speaker an issue in several competitive House races, given the controversial votes the chamber has held under her tenure, including ones on climate change and healthcare reform.

Kaine, meanwhile, declined to play political predictor, refusing to name how many seats his party may gain or lose this fall.