(CNN) On Thursday morning, with much fanfare (and tweeting), former Vice President Joe Biden's campaign announced that Michigan Gov. Gretchen Whitmer had endorsed his presidential bid.

Within hours, Bernie Sanders' campaign announced that the Vermont senator would cancel a planned trip to Mississippi on Friday and instead head directly to Michigan.

These things are not a coincidence.

Michigan, which will hold its primary on March 10, is not only the biggest delegate prize of that day ( 125 delegates ) but also hugely important, symbolically speaking, given that it was one of three critical Midwestern states President Donald Trump flipped to his side in the 2016 presidential race.

In 2016, the Michigan primary was similarly critical. Former Secretary of State Hillary Clinton, who had support from virtually every elected official in the state, was widely expected to win and, in so doing, effectively end Sanders' upstart campaign.

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