Detroit Mayor Mike Duggan is deep in campaign mode for Vice President Kamala Harris. The Democratic nominee for president is set to return to Detroit on Monday for a Labor Day event with her running mate, Minnesota Gov. Tim Walz. Like some other urban mayors across the country, Duggan is using his political pull to help mobilize voters in his city. That political muscle could make a difference in swing-state Michigan, a top prize for Harris and former President Donald Trump, the Republican nominee, in November’s presidential election.