evidence: Former President Donald Trump has of late become an advocate for Americans getting Covid-19 vaccinations. It’s not that Trump, in testifying to the vaccines’ scientific efficacy and lifesaving powers, has suddenly developed a sense of public-mindedness all too missing in his presidency. Rather, it’s a classic case of doing the right thing for the wrong reasons. [...] Trump didn’t name his target. But Florida Gov. Ron DeSantis, a rising GOP star and oft-mentioned potential 2024 Republican presidential candidate who is building his national image in Trump’s pugilistic image, has dodged questions about whether he has received a Covid vaccine booster. [...] But Trump is betting that the cult of personality around him is still strong enough to withstand differences on the vaccine and keep his supporters in line, propelling him to the 2024 GOP presidential nomination. He may very well be right. Trump in his vaccine messaging is effectively reminding DeSantis and other potential 2024 GOP challengers — like his former vice president, Mike Pence — who’s boss in the Republican universe.