Democrat Kamala Harris raised questions about Republican Donald Trump's physical stamina to serve effectively as president as the two rivals tore through the deadlocked battleground state of Michigan on Friday, with Trump lashing back about the energy he's shown on the campaign trail.

Harris, who turns 60 on Sunday, pressed the case to raise doubts about the 78-year-old Trump. Age had been an issue when President Joe Biden, 81, was still in the race, but had faded after he dropped his election bid.

Harris said on Friday news reports that former President Trump was skipping interviews because he was tired and had passed on the chance of a second debate with her raised questions about his fitness for office.

"It should be a concern. If he can't handle the rigors of the campaign trail, is he fit to do the job?" she told reporters before a rally in Grand Rapids. "That's a legitimate question."

Trump has skipped some appearances, but his campaign has not provided reasons.

Trump, talking to reporters as he arrived in Detroit, rejected such talk. "I've gone 48 days now without a rest," he said. "I'm not even tired. I'm really exhilarated. You know why? We're killing her in the polls, because the American people don't want her."

Polls in the election's most competitive states are effectively tied with just 18 days remaining until the election.

In a Fox & Friends interview, Trump also griped about negative television ads on Fox about him and said he would ask Rupert Murdoch, the founder of News Corp and who also launched Fox News, to ensure such ads are not broadcast until Election Day on Nov 5.

"I'm going to say, 'Rupert, please do it this way and then we're going to have a victory, cause everyone wants that,'" Trump said.

Trump visited a campaign office in Hamtramck, where he heard praise from the Detroit suburb's first Muslim mayor, Amer Ghalib. Trump was seeking support from Arab Americans in Michigan disenchanted with Democrats, Harris and Biden over U.S. support for Israel in the Gaza conflict.

"We all ultimately want one thing. We want peace in the Middle East. We're going to get peace in the Middle East. It's going to happen very fast. It can happen with the right leadership in Washington," Trump said, without elaborating.

In Oakland County, Harris welcomed members of the Arab American community to her rally and touted prospects for peace in the aftermath of the death of Hamas leader Yahya Sinwar.

In the evening, Trump returned to Detroit, Michigan's largest city, for a rally after saying on Oct 10 that the rest of the U.S. would turn into Detroit if Harris won.

There, Trump's microphone stopped working and the former president roamed around the stage for some 20 minutes.

"I won't pay the bill for this stupid company that rented us this crap," Trump said after the audio started working again. "This is the worst mic I've ever had in my life."

The dead-mic incident took place days after Trump stopped talking and swayed and bopped to his musical playlist at a Pennsylvania town hall event after two people in the audience fell ill.

Harris, after speaking in Grand Rapids, the heart of more conservative western Michigan, headed east to Lansing and then Oakland County, encompassing suburbs northwest of Detroit, on Friday night.

The Midwestern state has about 8.4 million voters and would bring the winner 15 Electoral College votes out of the 270 needed to win, which could be a decisive number. Harris and Trump are battling fiercely for the state's Arab American, senior, union and working-class voters.

Public and internal campaign polls show razor-thin margins for either Harris or Trump in Michigan and other battleground states. That is worrying Democrats.

Trump won Michigan by 11,000 votes in 2016. In 2020, Biden beat Trump in the state by 155,000 votes.

Harris is shifting the strategy of her whirlwind campaign to win over more Republicans and men of all races. She's also enlisting popular former first lady Michelle Obama, who will campaign for Harris in Michigan on Oct 26.

"I understand why people are looking to shake things up," former President Barack Obama said at an Arizona campaign event in support of Harris on Friday. "What I cannot understand is why anyone would think that Donald Trump will shake things up in a way that is good for you."

Nationally, Harris' edge has narrowed from a late September lead of 7 percentage points over Trump to just 3 points, Reuters/Ipsos polling shows, with high food and rent prices still worrying Americans and Trump amplifying fears related to migrants crossing the U.S.-Mexico border with increasingly extreme rhetoric.