WASHINGTON (AP) -- President Joe Biden picked up the endorsement of North America's Building Trades Unions at a Wednesday event where the president and his allies set out to dismantle Republican Donald Trump's reputation as a successful real estate developer.

"Donald Trump is incapable of running anything," said Sean McGarvey, the organization's president. "God help us if he gets anywhere near the White House in the future."

The event, held in a Washington hotel ballroom with a boisterous crowd of union members, was another salvo in the battle for votes from blue collar workers. Trump has tried to chip away at Democrats' traditional advantage with organized labor, while Biden has been adding to his roster of endorsements and trying to fend off his predecessor's comeback bid.

Biden said unions would help him make Trump a "loser again," and he mocked Trump's inability to pass infrastructure legislation when he was president, saying "he never built a damn thing."

The Democratic president repeatedly torched his likely Republican opponent as a callous businessman who turned firing people into entertainment as part of his long-running reality show "The Apprentice."

"He looks down on us. I'm not joking. Think about it," Biden said. "Think about the guys you grew up with that you'd like to get in the corner and just give him a straight left. I'm not suggesting you hit the president. But we all know those guys growing up."

Biden recently campaigned in his childhood hometown of Scranton, Pennsylvania, and he's increasingly used economic arguments to portray Trump as out of touch with workers' concerns.

In this election, Biden said, "it's either Scranton values or Mar-a-Lago values."

The endorsement adds to Biden's considerable union support. The United Auto Workers backed him in January, and the United Steelworkers Union followed suit in March.

A Trump campaign spokesman did not immediately respond to a request for comment. But Trump has also sought support from organized labor, including meeting with the Teamsters earlier this year.

"Usually a Republican wouldn't get that endorsement," Trump said. "But in my case it's different because I've employed thousands of Teamsters and I thought we should come over and pay our respects."

Trump's popularity with white working class voters has been a challenge for Democrats who puzzle over his appeal.

McGarvey promised "an unprecedented field program in key battleground states" to help defeat Trump this year.