Iowa Republicans have sunk a lot of time and resources into defeating longtime Democratic Rep. Leonard Boswell, and with winds at the GOP’s back, this could be the year it pays off. But state Sen. Brad Zaun wasn’t Republicans’ top choice, and after having trouble harnessing national and state momentum in his district, he has suffered a few costly stumbles.

On Thursday the Des Moines Register reported that in 2001 while Zaun was mayor of Urbandale, a suburb of Des Moines, police had to ask him to leave an ex-girlfriend alone. The article alleged that Zaun, who was divorced then but is now married again, came to the woman’s home after midnight and pounded on her windows, calling her names. When he followed up with a phone call, a police officer answered and asked him not to contact her again.

The article could not have come at a worse time. On the same day, Zaun took his previously scheduled turn on the Iowa State Fair’s soapbox and was forced to offer a mea culpa in a press conference afterward.

Regardless of Zaun’s weaknesses, Boswell can’t get comfortable. He hasn’t won more than 56 percent of the vote in his Des Moines-based district since before redistricting in 2000. Boswell, a 76-year-old farmer, has been dogged by rumors that he’ll retire and the suggestion that he has never quite fit his urban district. Since Democrats gained control of the House in 2006, Republicans have added the criticism that the Blue Dog is too close to Democratic leadership.

Boswell sees those criticisms as “nonsense” and “silly talk.” For one thing, he said, he’s younger than Sen. Chuck Grassley (R), who will turn 77 in September.

“I get up early,” he said in a phone interview last week. “I’m the first one in the office when I’m in D.C. I’m usually the last one there at the end of the day.”

He counters the idea that his agrarian roots make him less qualified to represent Iowa’s largest city, pointing to his time living there when he served in the Legislature from 1984 to 1996, and he argues that moving into the majority naturally means voting with his party more often.

“Some will say you’re with Pelosi too much,” he said of Speaker Nancy Pelosi (D-Calif.). “Excuse me, maybe Pelosi’s with me.”

Zaun, 48, wasn’t the obvious choice to retire Boswell. In the seven-way June primary, former Iowa State University wrestling coach Jim Gibbons had celebrity, national endorsements and better fundraising numbers on his side. Yet Zaun won with 39 percent to Gibbons’ 26 percent, and he won the support of all his primary opponents within a few days. Though up-and-coming Republicans in past cycles have gotten national support and continued to fall just short, Zaun thinks he can close the gap.

“Everything’s changed this time,” he said in a phone interview last week. He cited the likely Republican year and his base in Polk County, where the bulk of the district’s votes come from, as game-changers.

As he has worked his way up the political ladder, Zaun has never lost a race. He was first elected to the Urbandale City Council in 1996, served as mayor from 1998 to 2005 and then was elected to the state Senate. His first state Senate race was for an open seat in a Republican district and was the most expensive Legislature race in the state’s history, and he cruised to re-election for his second term.

Zaun has touted his bona fides as a businessman, first as a hardware store owner and now as vice president of a real estate agency, but that has become a bit of a liability. He has taken flak for paying off business-related debts right before he declared his candidacy but said that he dealt with the same type of problems others in the district have.

Boswell’s first ad of the campaign hit Zaun on his position on biofuels. In a radio spot that started airing last week, he used audio from a Zaun town hall during which the state Senator told a questioner that he would do nothing for the biofuel industry. The Republican said his comments were taken out of context, insisting he only wants to wean the biofuel industry off its tax incentives. Another of his comments was also taken out of context, he said: To those who say he is against flood relief help, he clarifies that he was only against help for the owners of a private dam that broke.

“What I object to is the government coming around after a disaster and handing out $10,000 debit cards, and I said years ago it was that neighbors helped out neighbors, and churches and nonprofits helped out,” he explained. “With that said, I do believe the government has a role.”

National Republicans have been slow to embrace the state Senator. He has been named only to the bottom tier of the National Republican Congressional Committee’s Young Guns program, and the third district wasn’t included in last week’s list of districts where the committee will place ad buys. Though Boswell had raised almost $1 million by the end of June, Zaun had only $240,000.

“I think they’ve been burned by spending a lot of money trying to beat Boswell in the past,” said Arthur Sanders, a professor of political science at Drake University in Des Moines.

Iowa Republicans enjoy having former Gov. Terry Branstad and Grassley at the top of the ticket, as they each lead polls in their races by double digits. Matt Strawn, chairman of the Republican Party of Iowa, called it the strongest lineup the party has had in a long time.

Ultimately, as what may turn into a Republican wave crashes over the heartland, Iowa prepares to lose a House seat in 2012, and for Boswell the squeeze may get a little tighter.