At the Philadelphia Convention, the most difficult challenge was the sovereignty of the states. The “monster sovereignty”, Washington had called it. In forming the federal government, were the states surrendering their sovereignty?
Sovereignty is supreme political power. The sovereign gets the final say, and cannot be overruled. I believe that the Constitution did not take away the sovereignty of the states, and the people. Rather, it made it collective. The states, and the people, remained sovereign, but only if they acted in concert with one another. This is statecraft of the highest order.
The power to unilaterally amend the Constitution gives the states, and the people, the final say, and makes them the collective sovereign. The power to amend includes within it the power to impeach. The states, and the people, could, theoretically, not only impeach the President, the Supreme Court, and the entire Congress. they could abolish them as institutions.
Except the Senate. Thanks to the last floor amendment, in the last hour, of the last day of the Convention, the Senate cannot be abolished. Governeur Morris proposed this amendment, and it passed without dissent.
This makes the states, and the people, as long as they act in concert with one another, the sovereign in our constitutional system. Other than abolish the Senate, and its equality of state suffrage, the states, and the people, can do anything. There is no appeal, no higher authority.
I say “the states, and the people”, advisedly. Because Congress can require that any amendment be ratified by the people, not by the state legislatures. If the state legislatures became, collectively, some sort of threat, any amendment they propose can be submitted to the people, acting in state conventions.
The retention of collective sovereignty by the states, and the people, is a feature, not a bug. As Hamilton summed up his case for ratification in Federalist 85, “We may safely rely on the disposition of the State legislatures to erect barriers against the encroachments of the national authority.”
Up until now, that reliance has been misplaced. Activating Article V with the Mason Amendment will change all that.
Let the erection of barriers begin.
reaganproject.com 
Your posts continue to be terribly misinformed. George Mason was clear that amendments were to fix defects. Thinking that a document being usurped, will, once changed, suddenly be obeyed, is pure balderdash.
Constitution re-writers purposely misquote Federalist 85. An Article V convention is not a barrier.
“Then it is important to strengthen the state governments: and as this CANNOT be done by any change in the FEDERAL CONSTITUTION, (for the preservation of that is all we need contend for,) it must be done by the states themselves, erecting such barriers at the constitutional line as cannot be surmounted either by themselves or by the general government. The only barrier in their power is a wise government….” (emphasis added)
— Thomas Jefferson To Archibald Stuart December 23, 1791