Technically he's correct. They could call a constitutional congress make a proposed amendment and get 2/3rds of the US people to vote to approve it.
Good luck with that though.
JOE: "I DO SOLEMNLY SWEAR THAT I WILL FAITHFULLY EXECUTE THE OFFICE OF PRESIDENT OF THE UNITED STATES, AND WILL TO THE BEST OF MY ABILITY, PRESERVE, PROTECT AND DEFEND THE CONSTITUTION OF THE UNITED STATES."; T R E A S O N; ALSO JOE: "NO AMENDMENT TO THE CONSTITUTION IS ABSOLUTE."