How can the constituion be changed?

Answer 1

There are 2 ways to change the U.S. Constitution.

The first way is for two thrids of both houses of Congress (the House of Representatives and the Senate) to propose a constitutional amendment. Once this happens, the proposed amendment is submitted to the states. The legislatures of 3/4 of the states must ratify the amendment. At this point, it becomes part of the constitution. The president has no official role in amendment the constitution (he doesn't have to sign the amendment for it to take effect, and can do nothing to defeat a constitutional amendment once it has passed). Of course, unofficially, presidents can use their political clout to influence public opinion one way or another, which can affect the chances of a constitutional amendment passing.

The second method starts with the states, and was likely included to give states a check on overreaching federal power. The legislatures of the states apply to congress for a convention to propose amendments to the constitution. If 2/3 of the states make such applications, congress must call the convention. Once such a convention is called, and amendments are proposed, the amendment(s) must be ratified by the legislatures of 3/4 of the states. This method has never actually been used to amend the constitution, but Congress has proposed amendments in response to threats by states to call a convention, likely to retain some control over the amendment process.