Republican Joni Ernst has pulled ahead of Democratic Rep. Bruce Braley in the Iowa Senate race, according to a new poll that points to a heated battle for votes in the final stretch.

The Quinnipiac University survey showed Ernst, a state senator, leading Braley by 6 points, 50-44 percent among likely voters. The poll also showed her leading among independents, a key voting bloc.

The results are a break from earlier polling which for months has shown Braley leading or tied with his GOP rival.

Peter Brown, assistant director of the Quinnipiac University poll, said in a statement put out by the university that while “some pundits back east” may have mocked Ernst’s ads in which she talked about living on a farm, “they send an effective message to Iowans that she is one of them.”

There are signs, though, that both candidates in the race are trying to moderate their message after a long stretch of nasty advertising. Millions of dollars’ worth of personal attack ads have been clogging the airwaves all year, but Braley and Ernst are suddenly reversing course.

For Braley, that means a new ad highlighting what campaign aides say is his "record of crossing the party divide" to help small businesses in the Hawkeye State. The shift in tone is also a sign he may have maxed out his base support and is looking to close the deal with moderate Iowans who are still on the fence.

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Ernst has a new ad of her own. In it, the Iraq War veteran describes herself as a "mom, soldier, and someone who really cares about the Iowa we leave for our children."

That's a far cry from earlier combative ads from Ernst, including one where she says she grew up on farms castrating pigs, and asks voters to send her to Washington to cut pork and "make 'em squeal." Ads like that catapulted Ernst to the top of a once-crowded GOP primary field, but they’re still being scoffed at by Iowa Democrats.

"Joni Ernst is known for what she does to hogs. But I gotta tell you, what scares me is what she wants to do to the people," retiring Democratic Sen. Tom Harkin said over the weekend at his 37th and final annual Steak Fry event, which Bill and Hillary Clinton attended. "The last thing we need in the United States Senate is another Tea Party zealot, who mocks people, refuses to compromise, and gets nothing done for Iowa."

Braley has been accused of mocking people, too. He got in trouble for insulting Iowa farmers when he was caught on tape at a fundraiser warning a group of lawyers and out-of-state donors that Iowa's senior GOP Sen. Chuck Grassley could become chairman of the judiciary committee if the GOP took the majority. "If you help me you may have someone with your background or you may have a farmer from Iowa who never went to law school," he said.

And while polls show Braley ahead with Iowa women, one of his earlier attack ads against Ernst dubbed "Peep" included video of a chick to tease her. The ad backfired, offending women in both parties. 

The latest polling suggests that the shadow of President Obama is having an impact on the race. Nearly three in 10 voters said the vote in the Iowa race is chiefly a vote against Obama. 

The Iowa race is critical. Republicans must flip at least six seats if they are to take back control of the Senate – that’s no sure bet, but bagging Iowa would greatly improve their chances.

The Senate race, though, was nevertheless widely overshadowed this week by another contest with no official candidates.  

Hillary Clinton, who is mulling a 2016 presidential run, on Sunday returned to Iowa for the Steak Fry for the first time since losing the 2008 presidential caucuses.

And on Wednesday, Vice President Biden makes a visit of his own.

He's in Des Moines to join the "Nuns on the Bus," who are part of a left-leaning Catholic social issues group kicking off a 10-state bus tour focused on voter registration. Biden’s office calls this an official visit and not political. But coming on the heels of Clinton's appearance, it is stoking speculation that he’s chasing the former secretary of State in getting some face time with Iowans.

In the Senate, race, the latest Quinnipiac poll of 1,167 likely voters was conducted Sept. 10-15. It had a margin of error of 2.9 percentage points. 

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