President Donald Trump’s allies are trying to contain a politically risky election year fight with Michigan Gov. Gretchen Whitmer as he struggles to balance presidential politics with a global pandemic in one of the nation’s most important swing states. Both sides have tried to de-escalate the feud this week, although Trump’s supporters in particular sought to downplay tensions that ratcheted up over the weekend when the Republican president unleashed a social media broadside against Whitmer, a Democrat who had been critical of the federal government’s response to the coronavirus outbreak. Trump has clashed with other Democratic governors as well, but...