Suppose first that Trump wins re-election, which is scary enough in itself. Then in the next election Pence runs as president with Trump as vice-president under the assumption that Pence would soon resign, allowing Trump to become president. If this worked, Trump could keep doing this and end up being president for life.

There is nothing in the Constitution that says that a person can’t serve more than two terms. The limit is only on how many terms they can be elected for.