President Donald Trump speaks to the media about the testimony to Congress of former special counsel Robert Mueller, Wednesday, July 24, 2019, on the South Lawn of the White House in Washington. (Jacquelyn Martin)

Corey Brettschneider is the author of “The Oath and The Office: A Guide to the Constitution for Future Presidents.” He is a professor of political science at Brown University and visiting professor of law at Fordham Law School.

In testimony before the House Judiciary Committee on Wednesday, former special counsel Robert S. Mueller III reiterated a central conclusion from his report: Under Justice Department policy, a president cannot be prosecuted while in office. He also emphasized a point lost on many Americans. Rep. Ken Buck (R-Colo.) asked Mueller, “Could you charge the president with a crime after he left office?” Mueller answered “Yes.” Buck, who seemed surprised, asked again whether Trump could be charged specifically with obstruction of justice. Mueller again said clearly, “Yes.”

Mueller’s answer needs to be front and center as Congress decides its next move. If the president is reelected and serves his full term, the five-year statute of limitations on obstruction of justice will run out before he leaves office. Thus, reelection would almost guarantee that Trump will never stand trial for his crimes. The only way Congress can ensure Trump is ever held accountable is to begin impeachment proceedings.

The first moments of Mueller’s testimony clarified a crucial point. Rep. Jerrold Nadler (D-N.Y.), the chairman of the Judiciary Committee, asked whether the special counsel’s report exonerated Trump on the crime of obstruction of justice. Mueller’s answer was a blunt "no." The 10 instances of potential obstruction of justice listed in his report kept Mueller from concluding that the president had not committed a crime. Rep. Ted Lieu (D-Calif.), who is a lawyer, even argued persuasively that the report built a strong enough legal case to sustain an obstruction of justice charge. Mueller, at first, agreed but later in the day declined to go that far: “We did not reach a determination as to whether the president committed a crime.”

That is because Trump is a sitting president, and therefore, per the internal Justice Department policy Mueller cited, cannot be indicted. As the report and Mueller’s testimony clarify, presidents can be indicted and put on trial after they leave office. The special counsel’s factual investigation, as Mueller noted in the report, was conducted “in order to preserve the evidence when memories were fresh and documentary materials were available.” Preservation implies that future action or accountability might be needed.

A legal loophole threatens to undermine this idea of criminal accountability. That loophole is the statute of limitations, which defines the length of time during which a person can still be charged with a crime after it has been committed. The statute of limitations for obstruction of justice is five years, meaning it would expire during Trump’s second term.

The statute of limitations is designed to ensure that no one faces an endless possibility for indictment. Prosecutors must indict or not within a reasonable amount of time. What the statute isn’t designed for is allowing criminal wrongdoing to escape punishment, yet that’s exactly what the Justice Department policy provides if Trump wins reelection.

So, the only way for justice to be served is if Trump is unable to complete a second term, which could occur if the president loses his reelection bid. But justice should not be left that much up to chance. Fortunately, there is another “constitutional process,” as the Mueller report calls it, to address presidential wrongdoing: impeachment. The only surefire way for the president to face real punishment for his acts of obstruction is if Congress decides to impeach and remove him. It is true that the time limit would still allow for a trial if Trump is impeached early in his second term, but impeachment takes time, and the longer the country waits, memories fade, and fresh evidence becomes stale. This is the best time to move forward.

Impeachment exists precisely for this purpose. Alexander Hamilton argued that presidents are immune from criminal prosecution while in office, but only because impeachment should come before indictment. Hamilton wrote that the president “would be liable to be impeached, tried, and, upon conviction . . . removed from office; and would afterwards be liable to prosecution and punishment in the ordinary course of law.”

This suggests different standards for impeachment and indictment. To impeach and remove a president, there does not yet need to be conclusive proof that a president committed a crime. It’s up to the House and Senate to decide whether the evidence suggests a crime was likely committed. If they do, impeachment will clear the path to criminal indictment after removal from office. If Congress fails to act, Trump will walk away scot-free. Absent impeachment, the Democratic mantra that “no person is above the law” will become meaningless.

Some Democrats argue that impeachment would ultimately fail and would imperil the Democrats’ chance of taking back the White House, but no one has a crystal ball that can predict the true effect of impeachment on the election. Moreover, the question of whether to impeach must be based on constitutional duty, not political considerations.

Near the end of Wednesday’s hearing, Rep. Veronica Escobar (D-Tex.) said, “This hearing has been very helpful to this committee as it exercises its constitutional duty to determine whether to recommend articles of impeachment against the president.”

Escobar is right to note this urgent imperative. If impeachment proceedings do not begin now, the president will be treated by our legal system as though he is above the law, empowered to use the office of the president to avoid legal consequences. The Constitution demands that justice be served; impeachment should now be the route to making sure it is delivered.

Read more:

The Post’s View: Mueller gave a warning on Russian meddling. Congress — and America — should listen.

Karen Tumulty: The real bombshell in Mueller’s testimony wasn’t about impeaching Trump

Henry Olsen: Mueller’s testimony crystallized public opinion against impeachment

Paul Waldman: Mueller all but confirmed that Trump committed obstruction of justice