The Constitution does not say that at all.

The Constitution gives Congress a great deal of oversight over how the executive branch is run. The President is supposed to execute the laws that Congress passes, spend the money that Congress appropriates in the way that Congress says it should be spent, etc. The President can't even appoint his own officials without the Senate's approval.

Beyond the Constitution, there is a long tradition of independent agencies running according to certain laws and principles that are laid out to them. The President is not supposed to directly order the people at these agencies what to do. Think the Department of Justice: you don't want the President ordering prosecutions. You want those decisions to be impartial. Trump just crossed a massive red line in dropping the prosecution of Eric Adams, and he did so purely in order to gain political leverage over Adams. Now, the NY mayor has to do what Trump says, or else Trump can order the DOJ to start prosecuting him again.

Trump has now openly declared on social media that he does not have to even follow the law, because he's "saving the country." He's trying to establish an elective dictatorship. Americans vote every 4 years, and whoever wins runs the entire government however they want, regardless of what the courts or Congress say.