The eternal question of U.S. politics rears its ugly ass again: "Why in the hell does anyone ever listen to Alan Dershowitz?"
No court can overturn a Congressional impeachment and conviction. Will somebody at Fox and CNN page the nearest genocidal torture-defending lawyer, who is either Alan Dershowitz or someone joining him on a search for the real O.J. Simpson killer at a five-star restaurant for lunch today, and get Dershowitz a copy of the United States Constitution?
The Constitution gives impeachment to the House and the trial to the Senate with the Chief Justice presiding. It gives the House the "sole" power of impeachment, and the Senate the "sole" power to try all impeachments. That means nobody else, least of all a different branch of government, gets to say anything at all.
The Constitution, pace Dershowitz, does not list all specific offenses that qualify for impeachment.
That nonexistent list does not include lying about semen stains.
Impeachment need not involve a crime and does not involve a court. According to the Constitution, "[t]he President, Vice President and all civil Officers of the United States, shall be removed from Office on Impeachment for, and Conviction of, Treason, Bribery, or other high Crimes and Misdemeanors."
Treason is a ground for impeachment whether or not barred by statute, because it is listed here in the Constitution, as is bribery. The fact that the charge of bribery should have Congress busy nonstop impeaching each of its members is not grounds for rewriting the Constitution. It's actually grounds for Congress to get busy impeaching each of its members.
"Other High Crimes and Misdemeanors" means abuses of power by people in high office. Any overlap with statutory offenses is coincidental. Lying to Congress may be a crime and lying to the public not, but the latter may be the graver high Crime and Misdemeanor. Contempt of Congress, a quintessentially impeachable offense on which an article was passed by the House Judiciary Committee against President Nixon, is not a crime for any court, but a high Crime and Misdemeanor enforceable by Congress, which for many decades literally held people in contempt by locking them up on Capitol Hill until they did as asked. The same committee voted down an article of impeachment on Nixon cheating on his taxes, since any old schmuck can do that. It's not an abuse of high office unless performed in a manner dependent on the power of the office.
The courts are not part of impeachment, but a separate court proceeding can follow. Guess who said the following.
"Judgment in Cases of Impeachment shall not extend further than to removal from Office, and disqualification to hold and enjoy any Office of honor, Trust or Profit under the United States: but the Party convicted shall nevertheless be liable and subject to Indictment, Trial, Judgment and Punishment, according to Law."
That's right, it was Alan Dershowitz, if he ever happened to accurately quote the U.S. Constitution.
The Constitution even spells out the punishment for impeachment and conviction. And it goes out of its way to make clear that impeachment and trials of impeachment and punishment for conviction belong solely to the legislative branch. In so doing, it refers to impeachment more often than virtually anything else, including when it bars presidents from pardoning those convicted:
"[H]e shall have Power to Grant Reprieves and Pardons for Offenses against the United States, except in Cases of Impeachment."
When the Constitution says that all trials shall be by jury (how's that working out?) it makes sure to specify: "except in cases of impeachment."
But Alan Dershowitz is arguably less certifiably insane on the topic of impeachment than most people.