"Checks and Balances. How Quaint!"
Congress passes a law empowering the Executive Branch to do unprecedented levels of spying on Americans thought to be trafficking with terrorists and foreign spies. The law sets up a secret court to authorize special warrants in those cases without delay and without compromising national security, but it makes any such spying WITHOUT one of those warrants a federal crime. A President signs that legislation into law. Several Presidents abide by it. Congress amends it to make it even more powerful. Another President signs that. More compliance. Lots of spying takes place.
9-11 happens. Congress asks the White House whether it needs the law made even more powerful. The White House says, "no thank you, it's working very well just the way it is, and besides, if it were broader it might be unconstitutional." (Which makes sense, because it IS a broad law already, and even in dangerous times the Constitution remains in force).
And, all the while, the White House knows full well that it's ignoring the law altogether, and wiretapping hundreds of thousands or even millions of Americans without any warrants at all, even secret ones.
What's a responsible Congress to do? Why, exercise oversight, of course! Find out what the hell's up, bless it if it's lawful, rein it in if it's not. Balance of powers, mutual jealousies, James Madison, Federalist Papers, all that stuff. Basic. Right?
Right. One day after the most pro-executive-power justice in modern history is sworn onto the Supreme Court, the White House tells Congress to screw off: it won't produce the documents behind its illegal decision to surveil Americans without warrants.
If the Founders shared one belief, it was this: that the accretion of power in a single Executive without meaningful checks posed THE greatest danger to the Republic. They had studied the failure of the Athenian democracy and the rise of the Roman Caesars, and they had lived under the careless hand of an uncaring monarch. And this -- this moderately paced but inexorable accumulation of power by an unaccountable executive -- was the foremost evil the Constitution sought to avoid.
Bad thing. If Congress doesn't do its job and force a showdown over these papers, WITHOUT recourse to an increasingly partisan and unreliable Supreme Court, then we need to replace the Congress. It's not a matter of politics, it's a matter of courage, and a matter of preserving the Republic.
Ask James Madison. He'll tell you.