The President does not have power of the purse. The House proposes a budget. The President can't spend beyond what Congress approves, and can't really decline to spend anything that Congress has approved (i.e. "impoundment").

> Because even if you make great progress; someone like a criminal president comes along and spends it all on favors.

That’s always a possibility, but as we’ve seen with the recent attempt to spend $500B to pay off student loans, the SCOTUS does a decent job of stopping the truly egregious.