The current political environment makes NAFTA worth considering. I haven't been able to find good research on this topic. I know that a country can withdraw from NAFTA by notifying the other parties to the agreement 6 months in advance. However, I haven't found any source that makes it clear how the United States would internally reach the decision. The US Constitution makes it clear the you need a 2/3 majority in the Senate to approve the ratification of a treaty. It's less clear whether the removal of or change of a treaty falls under that clause.
The North American Free Trade Agreement (NAFTA) is an executive agreement, not a treaty. As it was only passed with regular majorities of both chambers, it can be repealed or renegotiated with just the normal legislative process.
That is also true of treaties though. They can be repealed through the normal legislative process, as established in the Head Money Cases. Renegotiation would require a new ratification, but repeal does not.
It's also possible that the president can unilaterally remove the United States from a treaty. That's been done but never tested in court. It's possible that executive agreements like NAFTA have more protection, since as law, they would require the normal legislative process to repeal.