Last week, special counsel Robert Mueller -- who had been appointed by the Department of Justice two years earlier to investigate the nature and extent of Russian attempts to influence the outcome of the 2016 presidential election and to determine, if those attempts did occur, whether the Russians had any willing American collaborators in the Trump campaign -- came to the cameras and announced his resignation. He also underscored some of his findings and did so in such a manner as to gin up House Democrats in their march toward impeachment.

Since his nine-minute statement and his subsequent resignation, he has been praised by many in the political class averse to President Donald Trump, and harshly condemned by the president. He was even criticized by his longtime friend and former boss, Attorney General William Barr. Praised and criticized for what?

Here is the backstory.

JUDGE ANDREW NAPOLITANO: TO IMPEACH OR NOT TO IMPEACH

When Mueller confronted roadblocks during his investigation, he sought and received authorization from the DOJ to expand his investigation. The roadblocks consisted of attempts by the president himself to interfere with Mueller's work in order to keep Mueller's FBI agents at bay. Because of this behavior, the president, who originally was not personally a focus of the FBI investigation, became a subject of Mueller's investigation.

We learned from Mueller's report to Barr that while there is evidence of members of the Trump campaign collaborating with the Russians, there is not enough evidence to establish a conspiracy. We also learned that Trump personally engaged in 10 or 11 -- depending on how you count them -- efforts to interfere with Mueller's investigation. Each of these attempts at interference constitutes the crime of obstruction of justice. That crime consists of any material attempt -- whether successful or not -- to impede a federal investigation for a corrupt purpose. So, a lawyer who files motions asking a judge to restrain FBI agents from violating the lawyer's client's constitutional rights is interfering with a federal investigation, but for a lawful -- not a corrupt -- purpose.

Yet, when the subject of a criminal investigation orders those who work for him to lie to FBI agents or to falsify documents that are soon to enter FBI hands -- as Mueller found Trump did -- that constitutes an attempt to interfere with a federal investigation for a corrupt purpose. The corrupt purpose is not the vindication of constitutionally protected rights. Rather, it is keeping law enforcement away from the person who ordered the deceptions.

When federal law enforcement discovers evidence of presidential obstruction of justice, this immediately triggers two questions. The first asks whether the president can be prosecuted for these acts, as any other person would, and the second asks if these acts are impeachable offenses.

We know that presidential obstruction of justice is an impeachable offense because both President Richard Nixon and President Bill Clinton -- each of whom instructed aides to lie to FBI agents and falsify evidence -- were charged with it. The charges came in articles of impeachment. In these cases, either the House of Representatives or its Judiciary Committee found that the appropriate constitutional language that forms the basis for impeachment -- "high crimes and misdemeanors" -- includes obstruction of justice.

When Mueller gave his short farewell, he emphasized his view that this issue -- whether Trump's obstruction of justice warrants impeachment -- is squarely before the House. He did not argue that the issue of whether Trump in fact obstructed justice is an issue because his 448-page report laid out unambiguous evidence of Trump's obstruction.

Then Mueller addressed the issue of whether or not the president can be criminally charged while still in office. On that issue, he chose not to come to a conclusion, but to leave it to his boss, the attorney general, to do so. He did that knowing well that the attorney general -- who had just been appointed to his job by Trump -- was on record as having argued that a sitting president should not be charged with crimes. Mueller said publicly, however, that the reason for his personal hesitation in charging the president is an October 2000 DOJ legal memorandum. It offered that charging a sitting president with a crime would impair his ability to perform his constitutional duties and thus ought not to be undertaken.

But the 2000 opinion is just one of three that the DOJ has commissioned in the modern era. Of the three, two say the president ought not to be charged while in office, and one says that he may be charged. None says he cannot be charged.

Stated differently -- and this is no doubt what drew Trump's ire -- Mueller revealed in his farewell that, but for the 2000 DOJ opinion, there is ample evidence to have indicted President Donald Trump for obstruction of justice.

I have argued in this column and elsewhere that Mueller's deference to the 2000 DOJ opinion is misplaced. We know that because, two months after it was promulgated, federal prosecutors threatened to indict incumbent President Clinton for obstruction of justice on the day after he left office. Clinton chose to address the threat while still in office and directed his lawyers to engage in plea negotiations with prosecutors. They negotiated a plea deal in which he pleaded guilty before a federal judge Clinton had appointed to the bench. The plea was to ethical violations in which he admitted that he lied to the court.

Question: What do you call a threat by federal prosecutors to seek an indictment of the president, and subsequent plea negotiations? Answer: A prosecution of the president.

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Where does all this leave us?

Trump's legal woes are behind him. Impeachment is a political process that can only be successfully undertaken with broad public sentiment behind it. I doubt there is such sentiment today.

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