Trump is heading to Pennsylvania to make his case. So is Biden.

Former President Donald Trump is singling out Pennsylvania for his first rally of the general election on Saturday, where two of his most besieged candidates in the country are threatening to tarnish his record as a kingmaker.

The fact that he has zeroed in on the swing state for the politically symbolic Labor Day weekend, the unofficial kickoff of the midterms, demonstrates how pivotal Pennsylvania is to his success this year — and, more likely than not, a future presidential campaign.

Trump’s visit to the state also signals that he...