(CNN) Michigan Gov. Gretchen Whitmer , an emerging figure on the national political landscape, endorsed Joe Biden on Thursday, giving the former vice president a boost days ahead of his showdown with Vermont Sen. Bernie Sanders in her state's primary .

Whitmer also became a co-chair of Biden's campaign, making her the fourth Democratic official with the title.

"We need a president who will show up and fight for Michiganders," Whitmer tweeted Thursday morning. She said Biden "has proven time and again that he has our back. I am proud to both endorse him and announce that I will be joining his campaign as a co-chair."

We need a president who will show up and fight for Michiganders, and @JoeBiden has proven time and again that he has our back. I am proud to both endorse him and announce that I will be joining his campaign as a co-chair. pic.twitter.com/Vs5J4Ik09F

Michigan is expected to be the biggest battleground between Biden and Sanders next Tuesday, when its 125 pledged delegates are at stake in a primary that will be seen as a gauge of the candidates' electability in a state President Donald Trump won in 2016 and Democrats know they must flip to have a shot at victory in 2020.

Sanders defeated Hillary Clinton in Michigan in 2016, a win that rejuvenated his campaign at the time and turned the Democratic race into a long slog.

In 2018, Whitmer -- whose campaign slogan was "Fix the damn roads" -- defeated the Sanders-endorsed Abdul El-Sayed in the gubernatorial primary, and went on to trounce her Republican opponent by 9.5 percentage points just two years after Trump had won the state.

She has since become a rising Democratic figure who is widely seen as a prospect for the vice presidential nomination. She delivered the party's English-language State of the Union response this year.

"I think that the blueprint from 2018 on focusing on the dinner-table issues and getting things done is exactly what Joe Biden represents, and that's why he's got my enthusiastic support and my vote on Tuesday," Whitmer said on MSNBC, where she announced her endorsement.

Whitmer praised former President Barack Obama and Biden for expanding Medicaid and rescuing the auto industry, and said her mom had died of the same brain cancer that killed Biden's son Beau.

"Eighteen years ago I was taking care of my mom at the end of her battle with brain cancer and rearing my new child and fighting an insurance company that was wrongfully denying her chemotherapy. And I've got to tell you, I've commiserated with Joe about this very thing. He lost Beau to the same brain tumor that took my mom's life. And I know his commitment," she said. "And because of the work Barack Obama and Joe Biden did, I was able to expand Medicaid coverage to 700,000 people in the state of Michigan."

"When someone's seen a doctor for the first time as a result of the Medicaid expansion, it was the Obama-Biden administration that brought that to us," she said.

Whitmer had been under mounting pressure to endorse in recent days, and told reporters in Michigan that things had changed as the field consolidated and Biden racked up wins on Super Tuesday.

"As a candidate who's been written off, I saw what happened with Joe Biden and their ability to, you know, pick themselves up off the mat, dust themselves off and show the grit it takes to be successful. And bring others along. And I think that's what's so important too," she said.

Whitmer extended an olive branch to supporters of other candidates.

"Anyone who's supported Elizabeth Warren, she's fantastic. Same with Amy Klobuchar and Kamala (Harris) and Cory Booker and Pete Buttigieg. I mean, this is a group that has shown we are thinking about everyone in the American population, and we welcome all supporters -- Bernie's supporters as well," she said. "If and when Joe is the ultimate nominee, we're going to be the place where everyone can find a spot because we're fighting for the things that really matter to people's lives every day in this country, and we're going to get it done."