There is talk these days about a complex and somewhat arcane legal concept: obstruction of justice. The term refers, broadly speaking, to willful efforts to interfere with the operations of the legal process, including criminal investigations.

Let’s bracket the hardest definitional puzzles for now and ask a question that could become pressing before long: What happens if special counsel Robert Mueller concludes that President Donald Trump has, in fact, obstructed justice?

In answering, we should take a vow of neutrality. We should not allow our views about any particular president — negative or positive — to color our understanding of the meaning of the Constitution.

It is possible that Mueller could try to indict the president. Any such effort would probably fail. Though the issue is unsettled, the Constitution is best read to grant the president immunity from criminal prosecution.

That leaves impeachment — the ultimate weapon given by the Constitution to “We the People.” Is obstruction of justice an impeachable offense? Most people think so. But the answer is not clear.

The Constitution makes the president impeachable for “Treason, Bribery, or other high Crimes and Misdemeanors.” As history shows, high crimes and misdemeanors are egregious abuses of presidential authority. As Alexander Hamilton put it, the “subjects” of impeachment involve “the abuse or violation of some public trust.”

America’s framing generation was focused on abuses of the powers that the president has by virtue of being president. If you want to know what the founders had in mind, read the Declaration of Independence, which formed the essential backdrop for the constitutional debates.

It follows that some crimes just aren’t impeachable. If a president jaywalks, drives recklessly or shoplifts, he has certainly committed a crime. But he has not abused the authority of his office in a way that would justify resort to the impeachment mechanism.

It also follows that some abuses are impeachable even if they are not crimes. If a president runs roughshod over people’s constitutional rights, or decides to take a vacation for two months, he can be impeached, even though neither of those actions violates the criminal law.

We should now be able to see that obstruction of justice, as such, is not necessarily a high crime or misdemeanor. If the president obstructs justice with respect to an investigation of recreational uses of marijuana by White House staff, an impeachment proceeding would almost certainly be absurd.

If, on the other hand, the president interferes with the operations of an investigation in a way that falls short of obstruction of justice, we might nonetheless have a “misdemeanor” within the meaning of the impeachable clause. Suppose the FBI is investigating a possible act of presidential treason or bribery. If so, serious interference with the investigation would be an abuse of authority, and it would count as an impeachable offense — whether or not the interference meets the technical standards for obstruction of justice.

We can see in this light that President Trump was off the mark when he tweeted: “It would seem very hard to obstruct justice for a crime that never happened!” Obstruction of justice can occur even if the investigation turns up nothing; the reason that obstruction is criminalized is to protect the integrity of the legal process.

For impeachment, the orienting principle is simple: Everything depends on the subject matter of the investigation that was allegedly obstructed.

We have been here before — twice.

The first article of impeachment against President Richard Nixon pointed to obstruction of justice in connection with the investigation of “the unlawful entry of the headquarters of the Democratic National Committee in Washington, District of Columbia, for the purpose of securing political intelligence.”

This article met the constitutional standard. Unlawful spying on one’s political opponents strikes at the heart of our democratic system. It is an abuse of authority for a president to obstruct an investigation into that kind of misconduct.

The third article of impeachment against President Bill Clinton alleged that he obstructed justice in connection with “a federal civil rights action brought against him in a duly instituted judicial proceeding” — specifically, a sexual harassment case brought by Paula Jones.

That is a serious allegation, but it did not point to an impeachable offense. It is categorically different from the egregious abuses of presidential authority that the founding generation deemed a legitimate basis for impeachment.

Some of Mueller’s questions for the president are focused directly on the question of whether he obstructed justice in connection with the investigation of Russia’s role in the 2016 presidential election. If Mueller finds that he did, it would be a very bad outcome for the president.

Even if a candidate for president did not collude with a less-than-friendly foreign power, or have any relationship with it, presidential obstruction of an investigation into that issue would be a serious offense — from the standpoint of the impeachment clause, at least as serious as the first article of impeachment against President Nixon.

It’s important not to get ahead of any fact-finding. Perhaps Mueller and his team will not find anything serious. But for the president’s lawyers, demonstrating that there was no obstruction of justice in connection with the Russian investigation should be the highest priority. Right now, nothing else is a close second.

Cass R. Sunstein is a Bloomberg Opinion columnist. He is the editor of “Can It Happen Here? Authoritarianism in America” and a co-author of “Nudge: Improving Decisions About Health, Wealth and Happiness.”