Based on there being too many people like you who pretend (lie) they are not going to vote for him and then do so.
If you really were not going to vote for him you would no longer unquestionably continue to support the party that he is unquestionably the leader of. But you are an amoral political hack so I do not expect any more out of you.
And you can continue to be dishonest about your vote. Your secret is safe with me.