As the investigation into the Trump campaign’s collusion with Russia, led by special counsel Robert Mueller, continues to close in on President Donald Trump, he has started discussing his ability to pardon, even arguing that he could pardon himself despite the long-standing determination to the contrary by the U.S. Department of Justice (DOJ). Trump’s legal team has made an equally baseless assertion with respect to his actions to impede the Russia investigation, claiming that “the President’s actions here, by virtue of his position as the chief law enforcement officer, could neither constitutionally nor legally constitute obstruction … and that he could, if he wished … even exercise his power to pardon if he so desired.”

This view is wrong: It is clear that the president can obstruct justice. And—as reflected in past precedent, a Supreme Court decision, and constitutional history—abuse of the pardon power can constitute such obstruction and be grounds for impeachment.

Since obstruction of justice is discussed in this column in the context of the constitutional remedy of impeachment, rather than in the context of violating a specific federal obstruction of justice statute, the question of whether a sitting president can be criminally indicted is not addressed.

The president can obstruct justice

Trump’s legal team argues that the president has broad law enforcement and pardon powers and that he cannot obstruct justice through the exercise of that lawfully granted authority. But it is well-established that an otherwise legal action taken with corrupt intent to interfere in an investigation can be obstruction, just as an otherwise legal action can be bribery if done in exchange for money. For example, the DOJ investigated President Bill Clinton’s pardon of Marc Rich, a fugitive commodities trader, to determine if there was bribery, obstruction, or other illegal activity connected to it—though the inquiry eventually resulted in no charges being brought.

There is no question that the president can obstruct justice and that such obstruction can form the basis for an impeachment. As Daniel Hemel, a University of Chicago law professor, notes, obstruction of justice was one of the charges leveled against King George III in the Declaration of Independence, making clear that “the founding generation did not believe that heads of state were immune from obstruction charges.”

More recent precedent confirms this view. The articles of impeachment for President Richard Nixon included an obstruction of justice charge, stating that he violated his oath of office and constitutional duty because he “prevented, obstructed, and impeded the administration of justice.” Nixon himself acknowledged that “obstruction of justice is a serious crime and would be an impeachable offense.” Drawing from the Nixon precedent, President Clinton was impeached for obstruction of justice stemming from a sexual harassment lawsuit. In that case, Trump’s own attorney general, Jeff Sessions—who was then a senator—argued that obstruction of justice was a basis for impeachment.

Obstructive pardons are grounds for impeachment

The president has broad authority to grant pardons, but doing so to undermine an investigation of himself and his associates would constitute obstruction of justice. As former U.S. Solicitor General Walter Dellinger has noted, “The fact that a person can be fired for any reason or pardoned for any reason does not mean that in certain circumstances the reason might not constitute obstruction of justice.”

Again, the Nixon precedent is telling. When the House of Representatives drew up Nixon’s articles of impeachment, it explicitly included that he obstructed justice through his efforts to use his clemency powers to undermine the investigation. The articles stated that Nixon had been “endeavouring to cause prospective defendants, and individuals duly tried and convicted, to expect favoured treatment and consideration in return for their silence or false testimony, or rewarding individuals for their silence or false testimony.” Specifically, Nixon had discussed offering clemency to one of the Watergate burglars in exchange for favorable testimony.

Case law and constitutional history further support that abuse of the pardon power is an impeachable offense. In Ex Parte Grossman, the U.S. Supreme Court discussed the broad power given to the president to pardon, saying, “The Executive can reprieve or pardon all offenses after their commission, either before trial, during trial or after trial, by individuals, or by classes, conditionally or absolutely, and this without modification or regulation by Congress.” But in the same decision, the court noted that an abuse of the pardon power to undermine the rule of law could lead to impeachment, stating that:

If it be said that the President, by successive pardons of constantly recurring contempts in particular litigation, might deprive a court of power to enforce its orders in a recalcitrant neighborhood, it is enough to observe that such a course is so improbable as to furnish but little basis for argument. Exceptional cases like this, if to be imagined at all, would suggest a resort to impeachment, rather than to a narrow and strained construction of the general powers of the President.

The Founding Fathers addressed the issue at hand more directly, as the possibility of the president abusing the pardon power weighed heavily on the minds of some. In an effort to assuage their concerns, James Madison noted that “if the President be connected, in any suspicious manner, with any person, and there be grounds to believe he will shelter him, the House of Representatives can impeach him; they can remove him if found guilty.”

There is no relevant authority suggesting that the president is immune from impeachment for abusing the pardon power. To argue such immunity would be to put the president above the law—the very monarchical system that was explicitly rejected when the United States of America was founded. As with any legal authority granted to a political official, the pardon power can be abused and, if so, the person who abuses that power can be held accountable.

Building the political will to hold Trump accountable

While there is no question that abuse of the pardon power is an impeachable offense, the determination about how to respond to such an action lies with Congress. Congressional leadership has shown little appetite to exercise meaningful oversight over President Trump or hold him accountable for his actions, but an abuse of the pardon power could spur action.

Attempting to pardon his way out of the Mueller investigation would be politically disastrous for Trump. There have been widespread efforts by conservative lawmakers to dissuade him from firing Mueller because of their fear of the political ramifications. They have also argued against Trump trying to pardon himself—a legally dubious action that the DOJ determined was outside the scope of the pardon power during the Nixon presidency—and using the pardon power to obstruct the Russia investigation. Sen. Lindsey Graham (R-SC) went so far as to say that a self-pardon “would destroy the party, it would destroy his presidency.”

Conservatives likely recognize that Trump pardoning his close associates would result in sweeping public condemnation. The president’s lawyer, Rudy Giuliani, noted how important public opinion would be to lawmakers’ decisions about how to respond to presidential abuse of power, saying, “Members of Congress, Democrats and Republicans, are going to be informed a lot by their constituents. So our jury … is the American people.” And the view of the American people is clear: Polling has shown that the vast majority of people oppose the idea of Trump pardoning his aides or family members. That includes Trump trying to pardon himself, which one poll showed that 86 percent of people oppose.

Trump pardoning aides in an attempt to end the Russia investigation would lead to demonstrations across the country, similar to those that would occur if Trump fired special counsel Mueller. At last count, there were more than 900 planned protests with more than 350,000 people committed to a nonviolent response to such pardons. People understand that there is something terribly wrong with the president trying to stop law enforcement from looking into his potential crimes by giving himself, his associates, and his family a Get Out of Jail Free card.

There is no legal basis for the claim that Trump is above the law. There is no question that obstruction of justice is an impeachable offense and no question that abuse of the pardon power can constitute obstruction. The only question that remains is how Congress would respond to such an act—particularly whether, in the face of sustained public outcry, Republican members of Congress would hold the president accountable for his abuse of power.

Sam Berger is the senior adviser at the Center for American Progress.