Trump’s clout on the line in Senate GOP primaries

Former President Trump’s grip on the Republican Party will face its biggest test in Ohio after Friday’s endorsement of JD Vance in a crowded GOP primary to fill the retiring Sen. Rob Portman’s seat.

Trump’s endorsement has proved important in some races, but has done little to boost candidates in others, making his bet on the underdog Vance a risky one.    

It might not be his only risk either. Strategists and neutral political experts say Trump could also roll the dice by making endorsements in two other competitive Senate primaries in...