MINNEAPOLIS — President Donald Trump was defiant in the face of an impeachment probe as he sought to convert the threat to his presidency into a political asset on the campaign trail Thursday, with biting attacks on potential Democratic challenger Joe Biden.

Facing an investigation provoked by his unprecedented call for Ukraine and then China to assist in digging up dirt on his political rivals, Trump continued to lay into Biden and his son Hunter, whom he has accused without evidence of trading on the vice presidency for financial gain.

“The Bidens got rich, and that is substantiated, while America got robbed,” Trump said.

The rally in Minneapolis was the first since Democrats began proceedings two weeks ago to remove him from office.

It served as a proving ground for the president as he tries to use the impeachment inquiry to energize supporters for his 2020 campaign by casting himself — and his supporters — as victims of Democrats in the Washington swamp.

“They want to erase your vote like it never existed,” Trump said. “They want to erase your voice and they want to erase your future.”

He added, “The Democrats’ brazen attempt to overthrow our government will produce a backlash at the ballot box the likes of which they have never ever seen before in the history of this country.”

Before Trump took the stage, his son Eric warmed up the crowd with an attack on the Bidens.

The younger Trump asked the crowd for an assessment of how Hunter Biden is feeling and suggested that the familiar Trump rally chant of “Lock her up” — directed at Hillary Clinton — become “Lock him up” instead. The crowd then chanted, “Lock him up, lock him up.”

Trump’s adult children have faced congressional scrutiny for their foreign business dealings while their father is serving as president and Trump still maintains ownership stakes in his family’s businesses.

The rally, scheduled before House Speaker Nancy Pelosi, D-Calif., announced the impeachment investigation, came at a pivotal moment for Trump. His campaign strategy is focused on motivating his core supporters, rather than trying to win over a diminishing number of undecided voters, and the resonance of his appeal to the faithful may determine his second-term chances.

Trump has lashed out in acerbic tweets and public statements at Democrats, the media and even some Republicans as impeachment has dominated the national headlines. He has claimed that he is the victim of a “coup,” although impeachment is a constitutional process, and accused Democrats of trying to undo the 2016 election.