Michigan emerged as the unlikely final battleground of the presidential race, as Hillary Clinton hurried to defend the traditionally blue state from Donald Trump’s do-or-die appeal to disaffected working-class voters while making her own pitch Sunday in Ohio with the help of King James.

On the last day before voters go to the polls, Mrs. Clinton and her top surrogate, President Obama, will head to separate rallies in Michigan, which hasn’t voted Republican for president since 1988 but this year is in the sights of Mr. Trump.

Mr. Trump, the Republican nominee, held a rally Sunday in Sterling Heights, Michigan.

“We will make Michigan into the manufacturing hub of the world once again, and no politician will do that. They don’t have a clue,” he said.

Mrs. Clinton made a last-ditch effort in the key battleground state of Ohio, calling on Cleveland Cavaliers star and Buckeye State native LeBron James to urge voters to choose her over Mr. Trump.

Appearing alongside Mr. James at a campaign rally in Cleveland, Mrs. Clinton told Ohioans to reject the “dark and divisive” vision of her Republican opponent’s America, vowing that as president she would raise taxes on the rich to fund debt-free college for most Americans, more affordable child care, and massive spending on clean energy such as wind and solar power.

In Ohio — where polls have consistently shown Mr. Trump with a narrow lead — the former first lady is counting on Mr. James to help pull undecided voters off the fence and to whip up enthusiasm for her candidacy.

Addressing the crowd for only a few minutes, Mr. James said he believes Mrs. Clinton is best equipped to offer opportunity to the inner-city children he aims to help through his namesake foundation.

“This woman right here has the brightest future for our world,” said the three-time NBA champion and four-time league MVP. “The next thing I love, most importantly, is the fact that with my foundation and my inner-city kids, to give my kids the opportunity to feel like they’re important. With my foundation, giving my kids the notion someone cares about them can make their dreams become a reality is very important to me, and I believe this woman right here can continue that.”

In her own speech, Mrs. Clinton completely avoided Sunday’s announcement by FBI Director James B. Comey that the most recent probe into her private email server has been completed and that the FBI will not recommend any criminal charges.

Instead, Mrs. Clinton stuck to her normal campaign script, bashing Mr. Trump and promising to work on behalf of the middle class if elected.

Mr. Trump continued to use the issue, warning that Mrs. Clinton could not perform the duties of the presidency while being the “prime suspect” of an FBI investigation, predicting that she will eventually face criminal charges.

“If she was to win, it would create an unprecedented constitutional crisis. In that situation, we could very well have a sitting president under felony indictment and ultimately a criminal trial,” Mr. Trump told a rally in Sioux City, Iowa.

The Republican nominee pledged to bring real change to Washington. “Real change means restoring honesty to our government,” he said.

Mrs. Clinton’s appearance of Mr. James was part of a star-studded final few days for the Clinton campaign. Besides her Michigan effort, Mrs. Clinton will wrap up Monday night in Philadelphia with President Obama, Jon Bon Jovi, Bruce Springsteen and other noteworthy figures.

Pursuing blue-collar voters who tend to vote Democratic with his tough stances on trade and illegal immigration, Mr. Trump has made more visits to the Great Lakes state than any other Republican nominee at least since President George W. Bush in 2004.

Clinton campaign chairman John Podesta downplayed the significance of having to campaign in blue territory on the last day of the race. He insisted that shoring up support in Michigan was an offensive move, not a defensive posture taken in response to Mr. Trump’s targeting of a Democratic stronghold in the Rust Belt, which also includes Pennsylvania and Wisconsin.

Mr. Trump is competitive in all three states, especially Pennsylvania, where the race is a virtual dead heat.

Mr. Podesta said Michigan, coupled with a win in Nevada, could put Mrs. Clinton over the top of the 270 electoral votes needed to win the presidency.

“We’re going where the votes are. We’re going to finish strong. We feel good about Michigan and the rest of those states,” Mr. Podesta said on ABC’s “This Week” program. “We’re going to run through the tape.”

Republican National Committee Chairman Reince Priebus said a win by Mr. Trump in Michigan would put him over the top.

“If we win a state like Michigan it’s all over,” Mr. Priebus said on “This Week.”

Indeed, turning Michigan from blue to red would likely get Mr. Trump to 270 electoral votes. But he also likely can’t get there without flipping Michigan or another Democratic stronghold.

Mr. Priebus called the Michigan race “an absolute toss-up.”

The Real Clear Politics rolling average of recent polls in Michigan showed Mrs. Clinton 4.7 points ahead of Mr. Trump, 44.7 percent to 40 percent. The average included Libertarian nominee Gary Johnson at 6 percent and Green Party nominee Jill Stein at 2.5 percent.

The race has been tightening in Michigan as it has across battleground states and in national surveys. Mrs. Clinton and Mr. Trump were in neck-and-neck races in most swing states, including Florida, Ohio, North Carolina and Nevada.

Mrs. Clinton doesn’t necessarily need to win Ohio to win the White House, but a victory there would make her path much easier. The most recent Real Clear Politics average of all Ohio polls shows Mr. Trump with a 1.6-point lead; at least one recent survey by The Columbus Dispatch gave Mrs. Clinton a 1-point lead, though virtually all polls over the past week have been within the margin of error, suggesting a tight race in the final days of the campaign.

Mrs. Clinton continued to hold the lead in several national polls, as she has throughout the general election campaign.

The final NBC News/Wall Street Journal poll before the election gave her a 4-point lead over Mr. Trump, 44 percent to 40 percent.

Mrs. Clinton had an 11-point lead in the same poll in mid-October, 48 percent to 37 percent.

An ABC News/Washington Post poll gave Mrs. Clinton a 5-point advantage over Mr. Trump, 48 percent to 43 percent.

However, Mr. Trump held a 1-point lead over Mrs. Clinton, 44 percent to 43 percent, in an Investor’s Business Daily/TechnoMetrica Market Intelligence poll, which has been the most accurate poll in recent presidential elections.

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