In November, I wrote a column headlined “The case against indicting Trump.” I noted that most of President Trump’s misconduct in office, though appalling, was likely not criminal. I argued that policy reasons counseled against a new administration’s prosecuting a departing president even in cases where criminality might be a closer call, such as Trump’s obstruction of the Mueller investigation.

But I also noted that a policy of not prosecuting a former president should not be an absolute rule; it would be unimaginable to consider a president who committed a violent crime or sold U.S. secrets while in office as immune to prosecution. “But the bar has to be very high,” I wrote, and two months ago I didn’t think Trump’s actions as president, however odious, cleared that bar.

Well, in his final weeks in office, Trump has hurdled over that high bar. After Wednesday’s riot at the U.S. Capitol, it’s time for a criminal investigation — one that includes Trump himself.

While Congress was tabulating the electoral college votes to confirm the election of Joe Biden, a mob of pro-Trump rioters forced their way into the Capitol. They threatened the safety of lawmakers and staff, forcing them to take shelter. They broke windows, carried off property and posed for selfies. One of the insurrectionists died after being shot by police. It was more than six hours before law enforcement was finally able to secure the building and Congress was able to resume its work.

This riot, of course, did not happen by accident. For weeks, Trump and his allies whipped up his supporters by spreading false claims of election fraud. On Dec. 19, he tweeted, “Big protest in D.C. on January 6. Be there, will be wild!” On the day of the riot, he addressed the mob at his “Save America” rally, telling them they were going to “stop the steal” and prevent Democrats from “fraudulently taking over our country.” The president urged them to show “strength” and march to the Capitol, falsely promising he would be there with them (he actually retreated to the White House and watched the developments on television). As the riot unfolded, Trump reportedly resisted requests from D.C. Mayor Muriel E. Bowser (D) to deploy members of the D.C. National Guard to restore order.

The policy against criminal investigations of a former president for actions taken while in office recognizes that presidents often have to make difficult choices. We want to avoid the risk of criminalizing political differences. But that understanding has nothing to do with what happened at the Capitol. It’s impossible to characterize Trump’s incitement of the riot as having anything to do with the legitimate exercise of his executive power — just the opposite. A president who so debases his office and threatens the very foundation of government cannot take refuge in a policy aimed at preserving the dignity and orderly functioning of that government.

A number of federal statutes potentially apply to Trump’s actions. The crime of rebellion or insurrection provides that a person who “incites . . . any rebellion or insurrection against the authority of the United States or the laws thereof, or gives aid or comfort thereto,” may be punished by up to 10 years in prison. The crime of seditious conspiracy provides a 20-year penalty for anyone who conspires to oppose the government by force or “by force to prevent, hinder, or delay the execution of any law of the United States.” Inciting a mob to “stop the steal” by obstructing Congress’s certification of the election results seems to fall comfortably within either of these prohibitions. Other statutes no doubt could come into play as well, and an investigation would help make that determination.

The investigation should not be limited to Trump; others are potentially implicated in a conspiracy charge, as well. For example, the president’s personal lawyer, Rudolph W. Giuliani, also addressed the rally, exhorting those gathered to settle the dispute over the election via “trial by combat.” The actions of other Trump allies also should be thoroughly explored.

There may be potential defenses, of course. Trump and others may argue that the First Amendment safeguards their exhortations to the crowd. But just as there is famously no right to yell “fire” in a crowded theater, speech aimed at inciting imminent violence or criminal conduct is not constitutionally protected. Or Trump may pardon himself on the way out of office, although it’s not clear that would be valid. Such legal issues would need to be confronted during the investigation — but there is a more than adequate basis to begin that investigation.

Many are urging Trump’s immediate impeachment or removal by invocation of the 25th Amendment. That should absolutely be done, as soon as possible. But it wouldn’t be enough. There must be a forceful response to this outrage beyond merely depriving Trump of his final days in office. After Jan. 20, the Biden Justice Department should convene a grand jury investigation of Trump’s unprecedented assault on America’s democracy.

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