A lot of our best institutions are based on gentleman's agreements. If our representatives must ignore the processes we've come to expect, because those processes were never actually written down or coded into law... Yeah, the president has an unbelievable amount of uncheckable power to make the government just not run as intended.

The basic hypothesis is that if the president did something treasonous, he could be arrested by the military, who are sworn to protect the Constitution.

He couldnt change the rules, because our legislators do that, and its all written in the Constitution. But he could fail to appoint people, appoint people to multiple cabinet positions, or some other weird ways to get around this.