When Sen. Bill Cassidy voted to impeach Donald Trump after the January 6 attack at the Capitol, the outgoing president faced the lowest approval ratings of his political career—around 38 percent, according to the Real Clear Politics polling average. Though Trump’s average now stands at a similar 40 percent, the figure doesn’t capture the mood of G.O.P. primary voters. That’s one reason Cassidy lost his primary battle in Louisiana on Saturday—and why many swing-district or swing-state Republicans face a tenuous situation in the general election. Standing in solidarity with Trump is good for the base, but might not be so great when facing the broader electorate.