Maybe not in the primaries, but a viable challenger could come from the Democrats. Michigan still went blue in the electoral college for the Presidential vote.

Then again, between gerrymandering and demographic shifts individual districts can become more OR less defensible to incumbents.

Michigan as a whole can go either way, but Justin's district is about as solidly republican as they come. Short of radical redistricting, that's not going to change (edit: I see that the 3rd district did become more balanced in the most recent redistricting, but it's still a pretty solid republican seat).