Kamala Harris and Donald Trump will both be scouring for votes in Michigan on Friday as they try to lock down support in the key political battleground.

Ms Harris, the Democratic vice president, is scheduled to begin her day in Grand Rapids for a rally with other Democratic leaders.

She then goes to Lansing, where she will speak at a United Auto Workers union hall and promote the White House’s record of supporting domestic car manufacturing.

Her final event of the day is a rally in Oakland County, which is northwest of Detroit.

Mr Trump, the Republican former president, has his own event in Oakland County in the afternoon before holding a rally in Detroit in the evening.

Michigan is one of three “blue wall” states that, along with Pennsylvania and Wisconsin, will help decide the election.

Mr Trump’s event in Detroit will be his first one there since insulting the city last week. While warning what will happen if Ms Harris is elected, he said that “our whole country will end up being like Detroit”.

The city spent years haemorrhaging residents and businesses, plunging into deep financial problems, before rebounding in recent years.

One challenge for Ms Harris in Michigan has been union support. Although traditionally a Democratic bloc, she has failed to win some key endorsements.

In addition, Arab American voters have been skeptical of Ms Harris because of the White House’s steadfast support for Israel’s military operations in Gaza.

Republican presidential nominee former president Donald Trump gestures as he leaves the 79th annual Alfred E Smith Memorial Foundation Dinner in New York on Thursday (Julia Demaree Nikhinson/AP)

Michigan Governor Gretchen Whitmer, a co-chair of Ms Harris’s campaign, said in an interview on Thursday that the expectation was always that “it was going to be a close election”.

“People are like, ‘oh it’s so close.’ And I’m like, have you not been listening for decades?” Ms Whitmer said. “Michigan is a divided state. And that’s why we don’t write off the reddest of areas on a political map. We show up.”

Kent County, where Ms Harris will start her day on Friday, leaned Republican for many years, and was won by Mr Trump by 3% in 2016. But Joe Biden won the county in 2020 and it has increasingly voted Democratic recently.