With recent polls showing her making significant gains, Katie McGinty turned away from her Democratic rivals in a debate Friday and instead took aim at Republican Sen. Pat Toomey as she tries to win her party's U.S. Senate nomination in Pennsylvania.

McGinty, who has closed ground on the Democratic primary's front-runner, Joe Sestak, said Toomey had "sold out the middle class" and that she would "be a faithful and firm vote, upholding Social Security" and would "stand with taxpayers against Wall Street excesses."

Later she accused Toomey of voting against numerous bills that included aid to veterans.

The moments represnted a shift for McGinty, who in more recent debates had attacked Sestak as she tried to cut into his lead and halt his momentum.

Sestak, in turn, criticized party leaders who have spent millions in efforts to boost McGinty into contention in the final weeks leading up to Tuesday's primary.

"I'm different -- I'm not a politician, I'm a public servant," Sestak said.

He also repeated, for the first time in a debate, his oft-told story of one party leader in Washington who, according to Sestak, told him, "whenever I tell you anything, the only answer will be 'Yes.'"

"But it's alright - because trust is the biggest deficit we have in America today," Sestak said. Voters "know the system is broken."

McGinty and Sestak are the two leading candidates in the fight for a nomination that has drawn unusually intense interest -- and spending -- from national Democrats, who see unseating Toomey as a key to winning back control of the Senate.

Sestak, a retired admiral and former Congressman from Delaware County, has led throughout the race, but the contest has tightened as McGinty allies, including including Democrats' national Senate campaign arm, poured more than $4 million into a television ad barrage.

Sestak has thrived on grassroots support, but party leaders see McGinty as the more reliable candidate.

Several Democratic operatives in Pennsylvania in recent days have said Sestak still had an edge -- but that the race was increasingly close.

The change in tone arose in just a few instances during a debate that otherwise covered mostly familiar ground.

The event, taped at WPVI's Philadelphia studios, was the last joint appearance featuring the four Democratic candidates before voters head to the polls. It will air Sunday morning at 11 a.m.

Sestak and McGinty, Gov. Wolf's former chief of staff, lead polls in a contest that also includes Braddock Mayor John Fetterman and western Pennsylvania spring manufacturer Joseph Vodvarka -- who was just restored to the ballot this week after a court fight over his candidacy.

Fetterman, who repeatedly cast himself as the "true progressive" in the race, said he still could win, despite lagging in polls and fund-raising.

"We're the green on the roulette wheel," he said, citing the many undecided voters left in the race. "I certainly would never describe myself as the front runner, but I do believe that there is a path" to victory.

After the debate, McGinty said she would provide "the most stark contrast" with Toomey in the fall.

"The public cares about where people stand on issues and for me it's critically important that they know there's a real choice here in terms of someone who can fully and thoroughly fight Pat Toomey," she said when asked if improved poll numbers affected her tactics.

She attributed her gains to more people paying attention to the race as the primary has approached. She also released another in a string of television ads touting President Obama's endorsement.

Toomey's campaign said McGinty, as part of the Wolf administration, had tried to pass "one of the biggest tax increases in Pennsylvania history" while Toomey "was a strong supporter" of veterans affairs reforms "and has worked tirelessly to save Pennsylvania jobs."

Sestak did not stop to speak with reporters when the debate ended.

Vodvarka, in his first appearance at a televised debate, promised to fight for U.S. workers by imposing tariffs on foreign goods, and repeatedly assailed politicians as "criminals."