Which action best illustrates the system of checks and balances in the United States government?

When President proposes a bill, a congress (both House and Senate first have to approve it. Then the president can sign the bill into law or veto it. If he vetoes it, Congress can override the bill and make it a law. The Judicial branch, though, can declare it unconstitutional.

War, or Treaties- President can make treaties and send troops, but Congress have to approve the treaty and war.