WASHINGTON – Joe Sestak gained ground over the past month while his opponents were stuck in place, according to a new poll of the Democratic primary in Pennsylvania's U.S. Senate race.

The Franklin & Marshall survey, released Thursday, found Sestak with support from 31 percent of Democratic voters, up from 21 percent one month ago. His closest rival, Katie McGinty, had 14 percent – statistically unchanged from the 13 percent support the poll found when she first entered the race in August.

The poll is the first released since Sestak and McGinty began advertising on television early this month.

Braddock Mayor John Fetterman registered 7 percent support, an insignificant change from February. Joseph Vodvarka, a recently declared candidate, had no support.

The four are vying for the Democratic nomination in the race to challenge incumbent Republican Sen. Pat Toomey in one of the country's most critical Congressional races, one that could determine control of the Senate. The primary is April 26.

National Democratic leaders have made a concerted push behind McGinty, but this survey shows Sestak, a former admiral and congressman from Delaware County, building a lead.

"While they've got the big names, I've got mine, and my name is doing mighty fine right now," Sestak told reporters Wednesday, just after Democrats' national Senate campaign arm endorsed McGinty and days after Sen. Bob Casey (D., Pa.) did the same.

McGinty, Gov. Wolf's former chief-of-staff, has insisted that momentum is one her side. Her campaign – and Franklin & Marshall pollster Terry Madonna -- stressed that the survey showed that 46 percent of Democrats are still undecided, leaving many votes still up for grabs.

UPDATED: "We feel very good about where we are in this campaign," McGinty said in a Thursday afternoon meeting with the Inquirer's editorial board. "We feel there's just tremendous momentum that we've been able to build."

She said the winner so far is "Mr. or Mrs. undecided" leaving her campaign "growth potential."

Madonna and other neutral analysts have said television could be the most important factor in a race that has so far been drowned out by presidential campaign news.

The poll was conducted March 14-20, a week after Sestak allies and McGinty both launched their first ads – though with relatively small buys. McGinty said Thursday her ads had only started rolling when the poll was conducted.

And she got some potential help Thursday with the political arm of the Service Employees International Union announced an ad buy for McGinty in the Pittsburgh market. The union said it was a "six-figure" purchase but did not specify the amount.

The biggest burst of TV activity is expected next month. Sestak has more money to spend, but the Democratic women's group EMILY's List has pledgd to lay out $1 million on McGinty's behalf.

Madonna told the Inquirer's Chris Brennan that Sestak benefits from the name recognition lingering from his 2010 run for Senate. Sestak's numbers, though, have climbed: from 15 percent in January, to 21 percent in February to 31 percent now.

The poll also showed that 35 percent of voters view Toomey unfavorably, against 30 percent who see him favorably, similar to what the survey found in February.

The senate primary portion of the poll surveyed 408 registered Democrats and had a margin of error of 4.7 percentage points. The full poll, including the question on Toomey, surveyed 828 registered voters, with a margin of error of 3.3 percentage points.

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