Unable to modulate his excitement for other people’s political battles — and, according to advisers, not understanding the distinct incentives for governors who run their own states and senators who have to work with him in Washington — Mr. Trump has plunged headfirst into contests that have done little but expose his own political vulnerabilities.

In the last month, two Republican candidates the president supported lost their off-year races for governor, puncturing his self-proclaimed role as kingmaker. But even his successes in the 2018 governor’s races have left him disappointed: The winners he championed, once in office, have defied his wishes and cast aside his allies, as recently as this past week…

[S]ince his election, Mr. DeSantis — once a congressman who frequently jabbed at Mr. Trump’s critics during the investigation by the special counsel, Robert S. Mueller III — has seemed fine bucking the president.

He has steered clear of public defenses of Mr. Trump, preferring not to spend his political capital by wading into national issues. He has indicated to reporters that he will be too busy to put much time toward helping Mr. Trump in his re-election battle.