As the dust settles on what some have referred to as "Tapegate," U.S. Sen. Tom Harkin is confident that the latest scandal over dirty tricks will not impede the Iowa Democrat's bid for a fourth term, despite a tough challenge from Republican Rep. Greg Ganske.

A poll taken by Research 2000 for KCCI-TV between Oct. 1 and Oct. 3 had Harkin leading by 51 percent to 42 percent. Another poll by the Des Moines Register between Sept. 21 and Sept. 25, as "Tapegate" was being reported, found Harkin with a 20-point lead.

"It's over, and the polls show it," said Sarah Leonard, a spokeswoman for the Harkin campaign.

But Harkin team confidence wasn't always so high. In those heady September days, it seemed that Republicans had a valid question about Harkin's integrity after it was revealed that his campaign had delivered to the media a secret tape made by a Harkin supporter.

It all started when Des Moines businessman Brian Conley, a longtime Harkin supporter, switched his party affiliation to Republican and got himself invited to a large, but closed Ganske strategy session held at a Des Moines hotel in early September. While there, he secretly put the meeting to tape, which he then slipped to a Harkin campaign staff member, who leaked a transcript to the press.

The tape made headlines, as did the flap that followed. After initially blaming the Ganske campaign for making up the story, the Harkin staffer admitted his involvement. He was fired and Harkin's campaign manager resigned, admitting that the plot was hatched by the "overzealous" staff member.

This week, prosecutors announced they were dropping the investigation and would not pursue formal charges against the senator's campaign.

Republicans had hoped that the tape would suggest a long history of political skullduggery on the part of the three-term senator, and that voters will finally get wise and would unseat him.

"He'll go to any length to win and I think for the people of Iowa, it turns them off," said Dan Allen, a spokesman for the National Republican Senatorial Committee.

But that doesn't seem to be the case.

Democrats say voters are looking for substance over scandal and have found it in Harkin’s record.

"People are concerned about the economy, health care and things like prescription drug coverage," said Robert Gibbs, a spokesman for the Democratic Senatorial Campaign Committee.

"Let’s be clear about one thing: no one in Iowa should question the honesty and integrity of Sen. Tom Harkin," Gibbs added.

Political observers say the polls suggest Ganske may not have gotten as much traction from the incident as he had initially anticipated.

"The most recent 'Tapegate' could have been more problematic for the senator, but it now looks like it's not going to be," said Nathan Gonzales, an analyst for the Washington, D.C-based Rothenberg Report, which on Friday moved Harkin into a more comfortable "clear advantage" election category.

"It doesn't look like Ganske is in a position to get over the top," Gonzales said.

"I thought Ganske would move up more because of this," noted Michael Barone, political analyst and U.S. News and World Report columnist.

But according to Curt Mercadante, spokesman for Ganske, the taping incident is the tip of the iceberg in terms of how far the senator will go to win an election. He said it was a matter of time before one of his tricks backfired, and urged Iowans to think hard before sending Harkin, 62, back to Washington.

"This goes to the greater issue of deception and lack of integrity by the Harkin campaign," he said, charging Harkin with engaging in "nasty and brutal" attacks.

This isn't the first campaign in which Harkin has been accused of dirty tricks. In 1996, the Harkin campaign was accused of engaging in a "push poll," in which the polls are skewed by leading questions.

In that case, the surveyor asked voters whether they would be more or less inclined to vote for Harkin's opponent, Rep. Jim Lightfoot, if they knew he would be indicted for child molestation after the election.

"He’s a guy who can launch some pretty tough attacks and can be pretty aggressive," Barone said.

Ganske, 53, who beat a 36-year incumbent for his House seat in 1994, has won his last two re-election bids handily, but has also been accused by the Harkin campaign of chicanery this time around.

They point to a recent ad featuring a 30-year supporter of Harkin claiming she is now backing Ganske. The supporter turned out to be an actress playing the role.

"Ganske went up with the first negative ad in this race," Leonard said. "So it's a bit disingenuous to be calling us negative campaigners."

National Republicans deny talk that they are pulling their focus away from the Ganske race after the late-breaking poll numbers.

"I don't think it's a race that we're considering a home run, but it's got potential and we’re going to keep paying attention to it," Allen said.