And, ultimately, have the power to shitcan the laws under Article I, Section VII of the United States Constitution:
"Every Bill which shall have passed the House of Representatives and the Senate, shall, before it become a Law, be presented to the President of the United States: If he approve he shall sign it, but if not he shall return it, with his Objections to that House in which it shall have originated, who shall enter the Objections at large on their Journal, and proceed to reconsider it. If after such Reconsideration two thirds of that House shall agree to pass the Bill, it shall be sent, together with the Objections, to the other House, by which it shall likewise be reconsidered, and if approved by two thirds of that House, it shall become a Law."
If the President really doesn't want something to happen, and the other side doesn't have the 66% + 1 vote to override, that's the way it's going to be.