KALAMAZOO, Mich. (AP) -- Michelle Obama challenged men to support Kamala Harris ' bid to be America's first female president, warning at a rally in Michigan on Saturday that women's lives would be at risk if Donald Trump returned to the White House.

The former first lady described the assault on abortion rights as the harbinger of dangerous limitations on healthcare for women. Some men may be tempted to vote for Trump because of their anger at the slow pace of progress, Obama said, but "your rage does not exist in a vacuum."

"If we don't get this election right, your wife, your daughter, your mother, we as women will become collateral damage to your rage," Obama said. "So are you as men prepared to look into the eyes of the women and children you love and tell them you supported this assault on our safety?"

The rally in Kalamazoo was Obama's first appearance on the campaign trail since she spoke at the Democratic National Convention over the summer, and her remarks were searing and passionate in their support of Harris.

"By every measure, she has demonstrated that she's ready," the former first lady said. "The real question is, as a country, are we ready for this moment?"

Obama added, "Do not buy into the lies that we do not know who Kamala is or what she stands for. This is somebody who understands you, all of you."

Although Obama has been a reluctant campaigner over the years, she showed no hesitation on Saturday as her speech stretched from the political to the personal. Obama said she fears for the country and struggles to understand why the presidential race remains close.

"I lay awake at night wondering, 'What in the world is going on?'" she said.

Her voice vibrating with emotion, Obama talked about the struggle for women to understand and care for their own bodies, whether it's their menstrual cycles or menopause. And she spoke about the dangers of childbirth, when a split-second decision can mean the difference between life and death for a mother and her baby.

"I am asking y'all from the core of my being to take our lives seriously," Obama pleaded.

Harris took the stage after Obama and promised the crowd that she would keep their interests in mind -- unlike Trump, who she accused of only being interested in himself.

"There is a yearning in our country for a president who sees the people, not just looking in the mirror all the time, but sees the people, who gets you and who will fight for you," she said.

After the rally, Harris went to Trak Houz Bar & Grill with Michigan Gov. Gretchen Whitmer, where they drank a locally brewed beer.

"I want to have whatever she's having," Harris said.

The politicians chatted and took photos with people at the bar. When they approached a table of young women, one of them burst into tears.

Before arriving in Kalamazoo, Harris visited a local doctor's office in Portage to talk with health care providers and medical students about the impact of abortion restrictions. One of them said they have patients visiting from other parts of the country where there are strict limitations on abortion, and another said she's worried that people won't want to practice in important areas of medicine because of fears about government intrusion.

"We are looking at a health care crisis in America that is affecting people of every background and gender," Harris told reporters before visiting the doctor's office.

Harris appeared with Beyonce on Friday in Houston, and she campaigned with former President Barack Obama and Bruce Springsteen on Thursday in Atlanta.

It's a level of celebrity clout that surpasses anything that Trump, the Republican nominee, has been able to marshal this year. But there's no guarantee that will help Harris in the close race for the White House. In 2016, Hillary Clinton lost to Trump despite firing up her crowds with musical performances and Democratic allies.

Trump brushed off Harris' attempt to harness star power for her campaign.

"Kamala is at a dance party with Beyonce," the former president said Friday in Traverse City, Michigan. Trump held a rally in Novi, a suburb of Detroit, on Saturday before a later event in State College, Pennsylvania.

Saturday is the first day that early in-person voting became available across Michigan. More than 1.4 million ballots have already been submitted, representing 20% of registered voters.

When Clinton was running against Trump, Michelle Obama inspired Democrats with the slogan "when they go low, we go high."

But this year, at the Democratic National Convention in Chicago, she adopted a more biting approach. She accused Trump of "doubling down on ugly, misogynistic, racist lies as a substitute for real ideas and solutions that will actually make people's lives better."

While Harris was with Obama in Michigan, President Joe Biden visited the Laborers' International Union of North America in Pittsburgh. He mentioned that Harris once walked a picket line with the United Auto Workers -- "she has a backbone like a ramrod" -- while Trump has undermined organized labor.

"He views unions as getting in the way of the accumulation of wealth for individuals," Biden said. "It's in labor's interest to defeat Donald Trump, more than any other race you've been in."

Biden's remarks to the mostly male audience referenced the gender divide that has been a consistent feature of this year's presidential race.

Speaking on Trump, Biden said, "I'm just gonna say straight up, he's a loser as a man."

He also said that women deserve more opportunities than they've received in the past.

"They can do anything any man can do, including be president of the United States of America," Biden said.