Mr. Trump’s temperament and erratic, confrontational style are part of the reason voters do not like him. The Public Religion Research Institute’s 2019 American values survey found that 33 percent of American adults say their vote will depend on the identity of the Democratic nominee. Of this cohort, two-thirds say Mr. Trump’s personal conduct makes it less likely they will support him. What keeps them from rushing into the Democratic column is uncertainty over the eventual nominee.

Mr. Trump has two ways he could regain his standing among independents and win over undecided voters. He can pray that Democrats nominate a candidate whose personality and policies independents find more unappealing than his own. Or he can modify the way he comports himself in public. It is telling that the least likely option is the one within Mr. Trump’s control.

Still, Mr. Trump has been occasionally willing to act in the traditional presidential manner he describes as “stiff.” He more or less stuck to the script as he barnstormed the country in the last days of the 2016 campaign, joking that his advisers had told him, “‘Stay on point, Donald, stay on point.’” His State of the Union addresses have been full of the typical ceremony, pomp and decorum. Some of his speeches delivered overseas — in Riyadh, Saudi Arabia, Warsaw and Normandy, France — would fit nicely in volumes of presidential rhetoric.

These are exceptions. More often, Mr. Trump has pursued a base-first strategy that rewards loyal constituencies at the expense of independents and moderates. By the 2018 midterms, he was no longer “on point.” During raucous campaign appearances, he devoted more time to migrant caravans than to the state of the economy. With so many Senate contests in favorable red states, that may have helped expand the Republican majority. But it also alienated the voters in suburban districts across the country who decide which party controls the House of Representatives.

For Mr. Trump to connect with the voters he has lost over the last three years, he would have to reduce the rally ad-libs about the Academy Awards and the lost 33,000 emails, limit his free-for-all exchanges with the White House press corps — and above all delete Twitter from his phone.

Mr. Trump has a greater chance of winning the Powerball than of taking these actions. He prefers to rely on his enemies, and his remarkable luck, to keep him in the White House.

Should he choose to, though — as his campaign did in a World Series ad — he can stress the six million jobs created under his watch. He can also talk about, as he did in Dallas, turning the Republican Party into the party of “the American worker, the American family” and “the American dream.” He can even remind people that “it’s also the party of Honest Abe Lincoln.”