The core “check” applied to the Constitutional Amendment process provided by Article Five is the process of ratification. The key element of ratification is that it gives the states direct influence over the implementation of a Constitutional change or Amendment.
In every form of federal law, states have, at best an indirect means of
influencing policy. Federal statutes are decided by Congress, whose members are elected on the State level, but while in office, operate without direct oversight over the State governments.
Federal administrative laws are proposed by agencies empowered by Congress, giving states even less influence over that process. Due to the overall importance of Constitutional Amendments, which are the laws by which all other laws in the country must answer to, the states are allowed to play a vital role in the ratification of these laws.
What ratification specifically is the means by which a proposed Amendment is legislated into being. It is similar to the President signing a bill into law or vetoing it, save that
the Congress lacks the power to override a State rejection of an Amendment. Ratification works as such: when an Amendment (changes to the Constitution do not always have to take the form of an Amendment, which is a codicil to the document itself, but they have always taken this form) is proposed by either a two-thirds vote of both the Senate and the House of Representatives or a specially convened Constitutional Convention (which has never actually happened under Article Five), then it goes to the states for approval.
For an Amendment to be approved, or ratified, it must pass by a three-fourths vote in all individual State legislatures. By current standards, that means all but twelve states have
to approve the Amendment. If it passes in the legislatures of three-fourths of all states, then it is ratified. If it does not, the proposal remains active for a seven-year period, during which legislatures are allowed to vote and re-vote for ratification if they so choose.
After this seven-year period, the Amendment is officially supposed to “die.” There have been instances where Congress has tried to extend the period for a bill, but the legitimacy of this practice has been questioned and has still yet to face judicial review.