Now is the summer of Republican content. The G.O.P. is confident and unified. Donald Trump has held a consistent and widening lead over President Biden in all the battleground states. Never Trumpers have been exiled, purged or converted. The Supreme Court has eased many of Trump’s legal travails while his felony convictions in New York seem to have inflicted only minimal political damage — if they didn’t actually help him. Best of all for Republicans, a diminished Joe Biden seems determined to stay in the race, leading a dispirited and divided party that thinks of its presumptive nominee as one...