MINNEAPOLIS — President Donald Trump ripped into Democratic rival Joe Biden and his son Hunter at a rally here Thursday night, saying Biden was only a good vice president because he "understood how to kiss Barack Obama's ass."

In his first campaign event since House Democrats launched a formal impeachment inquiry, Trump mocked Biden and his son at length, accusing them of being corrupt. Earlier, Trump's son Eric warmed up the supporters with an attack on the former VP and the crowd broke into a chant of "Lock him up!" at the mention of Hunter Biden.

"The Bidens got rich, and that is substantiated, while America got robbed," Trump said. "Sleepy Joe and his friends sold out America."

An NBC News fact check found there is no evidence of wrongdoing by either of the Bidens.

In a largely off-script remarks, where at one point he mockingly called himself a "son of a bitch," Trump strayed from his recent rally talking points to launch new attacks at his favorite foils, from the FBI to the media.

He laid into Rep. Ilhan Omar, a Democrat who represents the district Trump campaigned in, repeating internet conspiracy theories about her.

It has been a tumultuous week for Trump, beginning with even his closest allies in Congress excoriating his decision to pull back U.S. troops in Syria. A series of polls in recent days also have shown a growing number of Americans backing the impeachment inquiry.

Thursday brought its own new twist, with two associates of Trump's personal lawyer Rudy Giuliani being charged with campaign finance violations over donations they made to the Trump campaign-endorsed super PAC America First Action.

During past moments of pressure in Trump's presidency, White House aides have emphasized the importance of the "Make America Great Again" rallies around the country in improving the president's emotional state, saying the events energize and motivate him. Trump's more than 90-minute speech Thursday appeared to do just that.

But Trump didn't travel to the friendliest of venues— he was interrupted by protestors at least six times. Minnesota is a solidly Democratic state that Hillary Clinton won by 1.5 percentage points. Nearly two dozen groups planned protests, according to local news reports, and a giant baby Trump balloon was inflated across the street from where Trump spoke.

In the days leading up to the event, Trump and his campaign got into a feud with the Minneapolis mayor over who would pay the public safety costs for the event. The campaign threatened to sue the city for demanding more than $500,000 and indicated the mega-rally might need to be rescheduled. Eventually, the matter was resolved, but it’s unclear who will ultimately foot the bill.

Still, Trump's campaign is hopeful it can flip Minnesota. The campaign didn't invest substantial resources in Minnesota and he barely campaigned here in 2016, but there's a concerted effort to change that this time around, even though the state hasn't voted for a Republican for president since Richard Nixon.

Aides said the re-election effort already has two dozen paid staffers here and is planning to spend millions on the Minnesota get-out-the-vote effort after spending only $30,000 in 2016. Trump often wistfully talks about winning the state, arguing "one more speech" could have made all the difference.

This stop — Trump’s fourth to the state in 16 months — continues a recent trend for the campaign, flush with cash, of holding events in places it lost in 2016 in the hope of expanding the map next year.