WAUKESHA, United States: Donald Trump used a break in his hush money trial to stage back-to-back appearances in two Midwestern battleground states Wednesday - but kept his legal woes front-and-center as he accused President Joe Biden of weaponising the courts against him.

The former Republican president, who is running for a return to the White House, rallied supporters in Wisconsin and Michigan, among the most hotly contested states in his expected rematch with Democrat Biden in November.

The speeches featured all of Trump's go-to set-pieces, from complaints about environmentally friendly household appliances to apocalyptic warnings of a looming world war - but his evening speech in Michigan was notable for its vitriol.

"Every single thing he touches turns to s***," Trump said of Biden in a speech in Freeland, Michigan peppered with profane language about his criminal charges, his 2020 election defeat and his determination to win reelection in November.

Trump had already spoken in an afternoon rally in the Wisconsin town of Waukesha, where he railed against Biden's handling of the economy and immigration.

In both appearances he accused Democrats of "executing" newborn babies as he turned to the deeply divisive issue of abortion rights, and in both he revived baseless claims that Biden is behind the 88 felony charges he is facing.

"I've got to do two of these things a day," he told a sea of red hats at his Michigan rally.

"You know why? Because I'm in New York all the time with the Biden trial - a fake trial that all of the legal scholars say is a disgrace," he said in Michigan.

Trump regularly claims that his indictments - three for alleged cheating in elections and one for hoarding classified documents - are being orchestrated as part of a political witch hunt, but never offers any evidence.

The 77-year-old tycoon used his rare day on the stump to project his preferred image as a confident, seasoned campaigner, far from the Manhattan courtroom where he is accused of covering up payments to a porn star before the 2016 presidential election.

Trump is the first former US president to face criminal charges, and the trial appears to have annoyed him to no end.

For two weeks he has been sitting through long hours of witness testimony, visibly bored and angry at no-nonsense Judge Juan Merchan, who required him to be present - and then imposed a gag order prohibiting Trump from publicly attacking witnesses, jurors or court staff.

Before and after each day's proceedings, Trump has been addressing journalists outside, venting about his legal problems, the US economy, his wife's birthday and the "freezing" temperature inside the courtroom.

"He hates being there in court, where he is just another criminal defendant," political expert Larry Sabato from the University of Virginia told AFP. "He has no control and is not in charge."

Biden's campaign has not missed a chance to bait his opponent over his legal troubles - referring to Trump as "Sleepy Don" after reports from the courtroom that the Republican was nodding off during the proceedings.

The nickname evoked the "Sleepy Joe" taunt Trump has long used for Biden.

Biden has advanced in the polls since March, with the two candidates now running neck and neck.

But Trump and his supporters hope to harness the media attention surrounding the trial to fire up his base, and push his message that Democrats are destroying the country through negligence on border security and poor economic stewardship.

In Waukesha, the former president accused Biden of being too passive on the pro-Palestinian student demonstrations that have convulsed college campuses nationwide, and of allowing the country to be "invaded" by migrant hordes.

Although Trump is energised by his campaign rallies, he had not held a single one since the start of his trial on April 15, with the only planned event cancelled due to weather.

"I have come here today from New York City where I'm being forced to sit for days on end in a kangaroo courtroom with a corrupt and conflicted judge enduring a Biden Sideshow trial at the hands of a Marxist district attorney," he complained in Michigan.

 -AFP