Republican Rep. Liz Cheney on Thursday endorsed and plans to campaign for Rep. Elissa Slotkin of Michigan, the first time that the critic of former President Donald Trump who lost her GOP primary has crossed party lines to formally support a Democrat. Slotkin is competing against Republican state Sen. Tom Barrett in Michigan’s 7th Congressional District. Their race is considered a toss-up by both sides and one of the Republicans’ chief targets in their campaign to win the House majority on Nov. 8.