They cheered because he was doing things they liked, not because he was expanding executive powers. They knew full well that these actions could be undone by the next executive. No one is surprised by this. Obama was doing what he thought was right in the only way left to him: the Republicans controlled the other branches of government and were openly opposed to any compromise. The Republicans still control the Senate and the the courts and Trump, with their complicity, has neutralized all oversight of the executive branch, but it is in his character to rule by fiat, so here we are. What is more remarkable is how little Trump accomplished in his first two years despite controlling all branches of government.