But by the time Kamala Harris showed up in Redford Township on Friday, there was no endorsement waiting for her.
By a slim margin, the International Association of Firefighters declined to back any candidate, a reminder of the Democratic nominee's struggle to lock down the same support from organised labour that President Joe Biden won four years ago.
The Teamsters also baulked at an endorsement in September.
Harris is still gaining more endorsements than she is losing: national teachers unions, building trade unions, the AFL-CIO and the United Auto Workers backed the vice-president shortly after Biden ended his run for a second term.
Kamala Harris spoke to firefighters in Michigan after missing out on their formal endorsement. (AP PHOTO)
And the leader of the Michigan firefighters union, Matthew Sahr, showed up for Harris in Redford Township, although not to bestow the endorsement.
"We could have chosen to stay away. But what kind of message would that send?" Sahr said.
A union spokesman declined on Friday to comment beyond a previously released statement that said there would be no endorsement for Harris or her opponent, former president Donald Trump.
"The vice-president is proud to have the support of organised labour, including firefighters across key battlegrounds like those who joined her in Michigan Friday," Harris campaign spokesman Brian Fallon said.
"She is the only candidate in this race who always stands with workers and has fought to protect overtime pay, worker pensions, and the right to organise."
What unfolded nonetheless reflects the shifting loyalties in American politics as Harris vies with Trump for support among working-class voters who for years could be more solidly counted on to support Democrats.
Still, Harris did not mince words when she spoke at the firehouse, saying Trump "has been a union-buster his entire career" and would launch a "full-on attack" against organised labour.
Donald Trump and Governor Brian Kemp visited a hurricane relief centre in Evans, Georgia. (AP PHOTO)
Harris said Trump supported "right to work" laws that often make it more difficult to unionise, and said he had weakened federal employees' unions.
Harris also accused the former president of "making the same empty promises to the people of Michigan that he did before, hoping you will forget how he let you down".
Her remarks followed US dock workers suspending their strike in hopes of reaching a new contract, sparing the country labour unrest that could have rattled the economy.
The vice-president later addressed an evening rally in Flint.
She spoke after basketball legend Magic Johnson, who said "nobody is going to outwork her", and UAW president Shawn Fain, who described Trump as "a scab".
During a rally in Saginaw, Michigan, on Thursday, Trump said Republicans were now "the party of the American worker", glossing over his anti-union record as president.
The former president also made a trip to Flint in September in an event billed as focusing on the auto industry, a pillar of the battleground state.
Donald Trump blasted the Biden administration on national security during a rally in North Carolina. (AP PHOTO)
The two candidates have been in the same cities - and in some cases the exact same venues - within days or weeks of each other.
Trump spent Friday in Georgia with Governor Brian Kemp, the latest sign he has patched up his rocky relationship with the top Republican in a key battleground state.
The former president and the governor appeared in Evans, Georgia, standing before pallets of goods including bottled water, nappies and paper towels destined for victims of Hurricane Helene.
"I have no doubt that whatever can be done is going to be done," Trump said.
"It's a lot of effort. It's a very heartbreaking situation."
Later Friday, he held a town hall in Fayetteville in another storm-ravaged state, North Carolina.
Speaking to an audience comprised largely of people with military connections, he repeated his promise to fire "woke generals", blasted the Biden administration's chaotic withdrawal from Afghanistan and said he would make it easier for veterans to seek medical care outside the government healthcare system.
