Michigan holds its non-presidential primary on August 7. Candidates in major party primaries need 1,000 signatures to run for U.S. House. Republican Congressman Thaddeus McCotter, who has been in Congress starting in 2002, appears not to have submitted enough valid signatures. See this story, which says he submitted approximately 2,000. The story does not explain why he would have had such a low validity rate. Michigan does not have registration by party, so any registered voter is eligible to sign.
McCotter is a Republican. The 11th district includes the western suburbs of Detroit. Michigan permits write-in votes in primaries, but no one can be nominated who does not have a number of write-ins equal to 15% of the number of people who vote in that primary. A lesser-known Republican did get on the primary ballot, but the story suggests the Michigan Republican Party may recruit a write-in candidate in the primary, which could be McCotter himself. Thanks to Jeff Becker for the link.