How can an amendment to the Constitution be proposed?

An amendment to the Constitution can be proposed with the approval of two-thirds of each house of Congress. This method reflects the framers' intention to ensure that any changes to the Constitution have broad support, as it requires a significant consensus among elected representatives. By establishing this threshold, the framers aimed to protect the integrity of the Constitution from fleeting political trends and ensure that amendments would only be enacted when there is considerable agreement across different political factions.

The other options do not align with the constitutional process. A national referendum is not a mechanism recognized in the U.S. Constitution for proposing amendments, although it may be used in some states for other decisions. A simple majority in Congress is insufficient to propose an amendment, reflecting the need for a supermajority to ensure stability and careful consideration of constitutional changes. Lastly, a president's executive order does not have the authority to amend the Constitution, as this power lies solely with the legislative branch.