The problem for Trump is there is a third shadow candidate in the race called “did not vote” so it doesn’t really matter than his main base would vote for him regardless.
If he fakes Swift’s endorsement and she comes out and roasts him and fires up her base to vote, the amount of votes he gains by trickery will be really small while the amount of people Swift converts from not voting to voting against Trump will be larger.
And there’s actually some data to suggest Trump is losing part of his always-red base and the rats are abandoning a sinking ship at the moment as well.