Putin will remain in power for as long as he is physically alive. If he lives until 2036, he will have been in power in the Russian Federation for 36 years by then.
No, I think strategic nuclear weapons are completely out of the question because everyone understands—Putin included—that even tactical nuclear weapons would still represent a global symbolic strike. After that, no one would trade with him or maintain relations with him.
Trump will not admit his defeat, that’s absolutely certain. Because Trump is simply the kind of person who is built that way—that’s his style of doing things.