Democratic candidate presidential and former vice president Joe Biden, who I have long admired, is right in saying that he would refuse to comply with a Senate subpoena absent a court order. In making that statement, however, Biden has now taken the legs out from under the second article of impeachment voted on by the House against President Trump.

That article accuses the president of “obstruction of Congress” for doing essentially what Biden said he would do, namely demanding a court order before he would comply with what he believes to be partisan subpoenas issued by one chamber of Congress. The chambers involved are different, as Trump has refused to comply with subpoenas from House Democrats, while Biden said he would refuse to comply with subpoenas from Senate Republicans, but the principles and legal issues are strikingly similar.

Put another way, by echoing Trump, Biden has provided the president with an airtight defense to the second article. If Biden is not obstructing the Senate by his refusal to comply with a Senate subpoena, how could Trump be guilty of obstructing Congress by refusing to comply with the House subpoenas absent court orders? The shoe is now on the other foot and causing blisters for Democrats. It could also be uncomfortable for Republicans, who may have to acknowledge that Biden has a point.

To be sure, there are some differences in degree. Trump is the president, whereas Biden is a private citizen running to become president. But that important difference favors Trump, who has the constitutional power to invoke executive and other presidential privileges. Biden lacks any such power as a private citizen. All he can argue in his case is that the Senate subpoenas are improper because they are motivated by partisan political considerations. This is not a particularly compelling legal argument.

Another difference is that Trump made a blanket refusal, whereas Biden made a limited one. But the principle that every citizen has the right to challenge congressional subpoenas and demand court orders is the same. Not only is it the same, it is also an important aspect of our constitutional system of checks and balances and of separation of powers. The power to challenge Congress in the courts makes concrete the abstract notion that no person or institution, including the legislative branch, is above the law and is subject to judicial resolution. Both Trump and Biden have acted on this principle, and neither of them should be condemned for doing so.

The proper statement by Biden that he refuses to comply with a Senate subpoena absent a court order points to the partisan double standards that have dominated this impeachment process from the start and, even before that, when President Clinton was improperly impeached. In a more perfect and less partisan world, what Biden said would lead the House to reconsider and reject the second article of impeachment, which never was a proper ground in the first place. If they will not, the Senate must take what Biden said into account when evaluating the second article.

Biden has since tried to clarify his statement by saying that there is “no legal basis” for the Senate to subpoena him. However, Trump has made the same point about the House subpoenas. The clear implication of this clarification is that Biden would not comply with a subpoena that has “no legal basis” unless the courts compel him to do so. Ironically, the original statement that Biden made about not complying, even when taken with his clarification, may now give the Trump legal team a more compelling basis for calling the former vice president as a witness. He could be asked to justify his original refusal to comply with a Senate subpoena, and then be asked why the refusal by Trump is any more obstructive than his.

This all goes to show how critical the “shoe on the other foot” test is in a case of impeachment, and how difficult it is for partisans of both sides to comfortably wear shoes designed to fit only their political opponents.

Alan Dershowitz is professor emeritus at Harvard Law School and author of “The Case Against the Democratic House Impeaching Trump” and “Guilt by Accusation: The Challenge of Proving Innocence in the Age of #MeToo.”