Green Bay, Wisconsin - Donald Trump doubled down on his heavily criticized warning of a coming American "bloodbath" Tuesday as he told supporters US communities faced "plunder, rape and slaughter" at the hands of undocumented immigrants.

In some of his most inflammatory comments to date on border security, Trump accused President Joe Biden of unleashing "carnage, chaos and killing" in a country he said was flooded with drugs and besieged by foreign criminal gangs.

"I stand before you today to declare that Joe Biden's border bloodbath... it's a bloodbath, and it's destroying our country, and it's a very bad thing happening," he said in an apocalyptic campaign speech in Grand Rapids, Michigan.

"It's going to end on the day that I take office."

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The former president – who faces a rematch against Biden in November's election – spoke out as the Republican National Committee launched BidenBloodbath.com, a website warning of an "invasion aided and abetted by Joe Biden."

While addressing the potential loss of auto manufacturing jobs to foreign countries last month in Ohio, Trump warned if he wasn't re-elected, "it's going to be a bloodbath for the country."

Hours after Grand Rapids, he repeated his fierce messaging at a rally in Wisconsin, where he savaged Biden for allowing what Trump called "an invasion of our country."

"We will liberate this nation from crooked Joe and his migrant armies of dangerous criminals once and for all," he told supporters holding "Fire Biden" signs in Green Bay.

Biden's campaign and Democrats accused him of fomenting "political violence," prompting an indignant response from Trump aides who said it was clear the tycoon was using the term to describe economic devastation.

Trump is often criticized for using extreme language that experts fear increases the risk of violence, whether in social media posts about his multiple prosecutions or at his rallies.

He referred to undocumented immigrants accused of criminality as "animals" in his fire-and-brimstone Michigan speech, highlighting the killings of several young women allegedly by foreign nationals.

"Under crooked Joe Biden, every state is now a border state. Every town is now a border town," Trump thundered.

"Because Joe Biden has brought the carnage, chaos, and killing from all over the world and dumped it straight into our backyards."

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He vowed to stop the "plunder, rape, slaughter and destruction of our American suburbs, cities and towns," comments he reiterated in Wisconsin.

While undocumented border crossings hit record highs during Biden's presidency, violent crime – in Michigan and nationwide – has been dropping since it spiked under Trump during the 2020 Covid-19 pandemic.

The billionaire was aiming to jumpstart his campaign with back-to-back rallies in Michigan and Wisconsin, two swing states crucial to his bid to defeat Biden. The Republican, who faces more than 80 felony counts and has been in and out of court for much of the campaign, has pledged retribution against political enemies and quipped he would be a dictator "on day one."

But in his Green Bay speech Trump said it was Biden who imperils the democratic system.

"I'm not the threat to democracy. Joe Biden and the fascists that control him – and they do control him – are the real threat to democracy," Trump said.

The Democratic National Committee accused Trump of hypocrisy on immigration, pointing to his pressure on Republicans in Congress to tank a recent cross-party deal that would have secured the most stringent border security measures in a generation.

Tuesday's first address was something of a homecoming for Trump, who closed out his successful 2016 campaign in Grand Rapids, winning Michigan on the way to claiming the White House.

Biden flipped the state back to Democratic in 2020, but polls currently have Trump leading, and the election is likely coming down to the wire. It is also predicted to be tight in neighboring Wisconsin.

Biden has been on a blitz through the swing states in recent weeks, visiting Wisconsin and Michigan as well as Arizona, Nevada, North Carolina and Pennsylvania.

He holds a widening lead over his Republican rival in the fundraising stakes, while Trump is burning through money as he pays legal bills to battle multiple criminal and civil court cases.