If we review the 12th Amendment, we find that there is a requirement that the Vice President must be eligible to become President. This has led many to conclude that someone who has already been “termed out” as President could not serve as Vice President; however, this does not appear to be correct. The 12th Amendment only requires that an individual who is ineligible to become President cannot be Vice President. It does not say that someone who is ineligible to be elected President could be Vice President. Accordingly, the 22nd Amendment leaves open a loophole that an individual could be elected to the Vice Presidency (or the Speakership of the House), then rise to the Presidency.
Trump can run as VP forever and become president after elected President resigns.