They can override a presidential veto with a 2/3 majority vote in both assemblies of congress.
The President checks Congress when he vetoes a bill
Congress doesn't have the power of veto; the President has the power of veto.
Balance of power.
The bill only goes back to congress if the President vetoes the bill. The President lists the reasons he would not sign the bill.
If the president vetoes a bill, then Congress can override that vetoe, but the bill must go back to Congress to be approved with a majority vote.
He vetoes the bill.
If the President vetoes a bill, it can be passed over his objection by a vote of 2/3 of each house of Congress. This is known as "overriding" the President's veto, and in this case, the bill becomes law even without the President's veto.
Only the President has the power to veto federal bills. He vetoes a bill by sending it back to Congress with his objections.
To overturn the president's veto of a bill 2/3rds of the congress needs to approve.
Overriding the president's vetoes, voting in a bill, & declaring war.
The principle is called checks and balances
The president can veto any bill that congress submits to him. By refusing to sign a bill into law, the president can prevent a law of which he disapproves. If the president vetoes a bill, the congress can override the veto, but it takes a 2/3 majority vote to accomplish this. This is very difficult.