The answer is no, and if you look at Trump’s tweets you’ll see he doesn’t actually claim that he can. He said, “I will ask to hold up funding to Michigan” if it continues with its plans for voting by mail. He later said funding cuts wouldn’t be necessary, but even his initial comment was not quite the threat it’s being made out to be. He can “ask” for whatever he wants, as can anyone, but whether he has any chance of getting it is a different story. His tweet about Nevada, meanwhile, was ambiguous.
Sometimes the president makes claims of unilateral power that have no basis and that his administration does not try to back — for example, his claim a few weeks ago to have “total authority” to end state lockdowns. This time, Trump skipped a step by making it clearish at the outset that his words didn’t mean anything.