Trump won 46% of the popular vote nationally (much more than that in many of the states he carried). Are more than 10% of the people who voted for him in 2016 not going to vote to re-elect, and nobody who voted against him in 2016 has changed his mind and decided he likes him now?
Trump’s supporters aren’t deserting him. I’d worry if his number had plunged but its remained rock-solid.
His campaign can focus on expanding his base.