The 22nd Amendment basically states that a president can only serve for a maximum of 10 years. If they are VP for more than two years and take over the presidency then they can run for two more terms. If they have not served two years as VP and take over the office they can only run once for themselves. If President Trump is removed from office, then VP Pence can run for two terms of his own. Presidents Trump, Clinton, and Reagan have called this Amendment undemocratic and called for its repeal.
Historically Speaking 