WASHINGTON - President Obama and Vice President Biden endorsed Katie McGinty in Pennsylvania's U.S. Senate race Wednesday, adding the White House imprint to one of the country's most closely watched Senate races.

"Katie is a true champion for working families," Obama said in a statement released by the McGinty campaign.

It was a rare example of the president stepping so directly into a party primary - though one that doesn't always work. In 2010, Obama endorsed then-Sen. Arlen Specter in the Democratic primary for the same seat, but Joe Sestak ultimately won the nomination.

Sestak, a former admiral and congressman from Delaware County, is leading in public polling again this year, despite McGinty's raft of establishment backing. Democratic insiders argue that McGinty, Gov. Wolf's former chief of staff, gives the party the best chance against incumbent Republican Pat Toomey, but Sestak has a history of rallying grassroots support.

McGinty, Sestak, and Braddock Mayor John Fetterman are vying for the Democratic nomination in the April 26 primary and the right to remain in a race that could determine which party controls the Senate.

In a meeting with the Inquirer's editorial board, Fetterman said he was "stung" by the president's decision because he had endorsed Obama in 2008, when most prominent Pennsylvania Democrats backed Hillary Clinton.

"I'm not angry," Fetterman said. "I'm more sad because this is a person who I still think is a fabulous president."

He also ripped McGinty and Sestak as inauthentic, contrasting their careers with his work in Braddock, a Southwestern Pennsylvania borough ravaged by economic change and job losses.

"What in Katie McGinty's background or Joe Sestak's background gives any indication that they care about working-class families?" he asked.

In his endorsement, Biden hailed McGinty's blue-collar background in Northeast Philadelphia - she's the daughter of a restaurant hostess and a police officer - saying, "She knows what it means to work hard, struggle to make ends meet, and build a better life."

In a news release after the endorsement, Sestak said he and the president share common ground on many issues and "wear the same battle scars, with pride."

Responding to Fetterman's questions about his working-class appeal, Sestak's campaign said he had helped 18,000 constituents in his two years as a congressman and turned down lucrative lobbying jobs to focus on public service.

The Senate race wasn't the only Pennsylvania contest that drew Obama's interest. The president also endorsed Montgomery County Commission Chairman Josh Shapiro in the three-way Democratic primary for state attorney general.

In a statement released by Shapiro, Obama called him "a true progressive with a strong record of standing up for Pennsylvania."

Shapiro, who has known Obama since 2006 and endorsed him in 2008, said it is uncommon but not unheard of for a sitting president to offer an endorsement in a competitive party primary.

One of his rivals, Northampton County District Attorney John Morganelli, called Obama's endorsement "a joke" and knocked Shapiro's lack of courtroom experience.

The campaign for another candidate, Allegheny County District Attorney Stephen Zappala, said Shapiro "is calling in all the political favors he can."