Hmm...
I boxed in my 20s.
It’s actually like training for a particular fighter’s style and then getting one with a different style at the last minute.
If you’ve been sparring like you’re facing a dance around the ring guy and at the last minute he’s replaced with a brawler..that’s a lot of trouble.
The reason you are mistaken is because there are campaign finance contribution limits. (However, you point about different styles only emphasizes my point—the replacement will have already been focuses on Trump and will be fully armed with opposition research.)
Regardless, if Bernie can somehow miraculously survive until the GE, I very much hope he is the nominee because Trump would stomp him.