They'll invoke the 25th. He can write a response saying he is still fit, but that won't happen. Because that would make the cabinet members once again invoke the 25th and then two thirds would have to vote to remove him. He won't want it to come to that. For the good of the country (in his view) he'll resign. Plus, he knows he is tuckered out and can't perform the duties of President.He won't. It's all about pride for him and his legacy. They'll probably invoke the 25th. About as best of an excuse they're going to get to get rid of him.