I recommend this piece by Marty Lederman in its entirety, but the bottom line sums up why the argument about to get five votes from the Trump Court that Trump can refuse to comply with congressional subpeonas because they might “undermine” the presidency is absurd:
Do revelations of wrongdoing, or conflicts of interest, or bad judgment, “undermine” the president and other executive officials in the eyes of the people? Of course they do. And indeed, that’s often an objective of the investigation for at least some legislators, as it has been in virtually every high-profile congressional investigation in our history, from the St. Clair expedition to the Committee on the War in Lincoln’s time, to the Teapot Dome scandal, to Watergate, to Whitewater, to Iran/Contra, to Benghazi, and on and on.
On at least two occasions in the Mazars arguments, Wall stressed that the potential harm is not only that the subpoenas might “undermine” Trump, but that they could “harm and undermine the presidency of the United States–not just this president, the institution of the presidency going forward.” It’s deeply unfortunate, of course, when the presidency or any other of our institutions is tarnished by disclosures of the wrongdoing or malfeasance or negligence of those who hold office in them. But the fact that such things are brought into the light, thereby “undermining” the officeholder, is one of the most important functions of congressional oversight. As Justice Ruth Bader Ginsburg noted in the Vance argument, the Nixon tapes had a devastating impact on the president: He resigned from office—the ultimate “undermining.” But that was a feature, not a bug, of the Ervin Committee’s justly celebrated investigation.
Basically, this the same logic the Trump administration is applying to COVID-19 testing; if a president doing bad things will undermine the office, then the remedy is to avoid finding out about them. It would be embarrassing if even one Supreme Court justice voted for this transparent horseshit, let alone five, and yet here we are.