ATLANTA, United States (AFP)— Kamala Harris crisscrosses Michigan on Monday while Donald Trump heads to Georgia — another of the decisive swing states in one of the closest US elections in history — after presiding over a dark mega-rally aimed at whipping up his right-wing base.

With only a week until November 5 Election Day, more than 41 million Americans have cast ballots in early voting — including outgoing Democratic President Joe Biden, who voted on Monday after waiting in a long line in his hometown Wilmington, Delaware.

Tensions are soaring in a race that polls suggest is too close to call, fueled by fears that Trump could again refuse to recognise a defeat, as he did in 2020. The Republican continues to claim he was cheated, and his rhetoric has become increasingly infused with violence and threats.

Concerns increased after ABC News reported that a fire consumed hundreds of early ballots cast in a supposedly secure drop-off box in Vancouver, Washington, part of a highly competitive district. Arson was reportedly suspected in another ballot box fire hours earlier in Portland, Oregon.

Meanwhile, Trump faced outrage after one of the warm-up speakers at his Sunday rally in New York’s Madison Square Garden called majority-Hispanic Puerto Rico “a floating island of garbage.”

The former president’s campaign said this “does not reflect the views of President Trump.”

However, the speaker, comedian Tony Hinchcliffe, was unrepentant, writing on social media that critics “have no sense of humour” — a comment reposted by Trump’s son and advisor Don Trump Jr.

Harris, 60, called Trump “increasingly unstable and unhinged” in an interview with CBS News. She later told reporters that Trump “fans the fuel of hate.”

As the clock ticks down, the challenge for Harris and Trump is both to energise core supporters and pull in the tiny number of persuadable voters who might still tip the balance — especially in the seven swing states where polls suggest they are running neck-and-neck.

Harris, who spent Sunday in must-win Pennsylvania, was holding three events in Michigan, while Trump was to hold two in Georgia — a pattern set to be repeated around the country’s other battlegrounds for the next seven days.

On Tuesday in Washington, Harris will deliver what her campaign calls a “closing argument,” in a nod to her career as a prosecutor.

The Democrat will speak from the same spot near the White House where then president Trump stoked his supporters on January 6, 2021, to launch a violent assault on Congress in an attempt to stop certification of his reelection loss to Biden.

Trump — the oldest presidential nominee ever and also the first to have been convicted of crimes — used a packed Madison Square Garden for his own closing pitch on Sunday.

The campaign celebrated the event in the legendary arena as a show of force and energy.