A fired-up President Trump lashed out against Democrats at a combative campaign rally on Thursday night, deriding them as “very sick and deranged people” who were only investigating him for abuse of power in order to “erase your vote”.

Facing impeachment in the House, Trump took his case to his core supporters, arguing that Democrats were trying to overturn the 2016 election because they knew they could not beat him in 2020. He singled out former Vice President Joseph R. Biden Jr. as nothing but a toady for President Barack Obama.

“He was only a good vice- president because he knew how to kiss Barack Obama’s ass,” Trump said, a line that drew huge roars of approval from the crowd.

In his first campaign rally since Speaker Nancy Pelosi declared the formal beginning of an impeachment inquiry last month, Trump was as raw and rancorous as ever, targeting individual Democrats in highly personal terms that no President has used in public and presenting himself as a victim of a partisan conspiracy.

“From Day 1, the wretched Washington swamp has been trying to nullify the results of a truly great and democratic election,” Trump told a crowd of about 20,000 at the Target Center in Minneapolis, one of the most Democratic cities in the country. “They want to erase your vote like it never existed; they want to erase your voice, and they want to erase your future.”

He fired off insults in rapid succession at FBI agents, lawmakers and journalists who he said were out to get him. “She’s either really stupid or she’s really lost it — or maybe there’s a certain dishonesty in there,” he said of Pelosi.

Representative Ilhan Omar, Democrat of Minnesota, who is one of his favourite targets, is an “America-hating socialist” who married her brother in order to come into the country, he said. (No proof has emerged substantiating the marriage claim.)

He went local in targeting the city’s Democratic mayor, Jacob Frey, who drew the President’s ire this week for seeking reimbursement for the cost of extra security required for the rally. “You got a rotten mayor,” Trump said. “You’ve got to change your mayor.”

But no Democrat came under as much fire as Biden, one of the leading Democrats bidding to challenge him next year.

It was Trump’s efforts to pressure Ukraine’s President to come up with damaging information about Biden that prompted the House impeachment inquiry that now threatens his presidency.