President Donald Trump cannot have committed impeachable offenses in seeking to thwart or disparage Special Counsel Robert Mueller's investigation of his and his campaign's "collusion" with the Russians to manipulate the 2016 election. Trump's opposition to the Mueller investigation could not have constituted "obstruction of justice."

That's because Trump was the victim of a "malicious prosecution." As such, he was within his personal rights to defend himself against what was in effect defamation, by protesting his innocence and questioning the motives for the prosecution.

English and American law has long tried to restrain abuse of police, prosecutorial and judicial processes by giving the victims of such abuses a remedy in damages from those who instigate or abet "malicious prosecutions."

The grounds for seeking damages after a prosecution are: 1) that no proper probable cause existed to start the prosecution; 2) that the effort produced no finding of criminality, and 3) that the victim's accusers acted out of malice.

An action for malicious prosecution involves similar standards to a civil suit for defamation by a public figure. The plaintiff needs to show: 1) falseness in the accusation and 2) actual malice on the part of those making the false allegation.

The Mueller probe of collusion with Russia was undertaken without proper probable cause. The grounds for the accusation of wrongdoing came from the Steele dossier, which is false and defamatory.

Second, the Mueller report found no collusion-related crime on Trump's part or his campaign's.

The third element supporting a claim of malicious prosecution, malice in the accusers, is easily shown.

Steele himself is known to have despised Trump. The public statements of John Clapper and John Brennan about Trump colluding with the Russians show malice. The private e-mails between FBI agent Peter Strozk and his mistress reveal their disdain for Trump and their fear of his being elected president.

The efforts by the Clinton campaign and other Democrats to promote the Steele dossier with the FBI and others show at least political animosity toward Trump verging on malice.

Former FBI Director James Comey's distaste for Trump when he provoked Mueller's appointment as special counsel is recorded in his memoir.

Thus, there seems to have been plenty of what the law considers malicious intent on the part of all those who ginned up the grand jury investigation into Russian collusion.

Now, the law of malicious prosecution has one very large loophole — government prosecutors are given personal immunity and can't be sued for any malicious prosecution they undertake. Thus, Trump can't sue Mueller and members of his investigation team for the tort of malicious prosecution.

So the law leaves a vacuum where irresponsibility can thrive among prosecutors. We should wonder how Mueller and his team would have behaved had they needed to worry about being sued after their investigation was completed.

Given the law of malicious prosecution, once Mueller determined that there was no collusion, he should have called off the investigation and reported to the people that he had found no crime. He should not have gone on to pursue obstruction of justice evidence against Trump. Without an underlying crime, there was no "justice" to be had in further pursuing targets just to vilify them or concoct grounds for impeachment.

In retrospect, Trump's opposing from the beginning defamation of his character through false accusations of criminality did not constitute obstruction of any legitimate legal process. It was a rightful act of self-defense — not an impeachable offence but normal political combat — as high-minded or as heavy-handed as the tactics might be.

Just because a prosecutor assumes righteous authority to accuse any one of us of crimes, this does not make accusations true. We are all innocent until proven guilty in a court of law. Speaking out against a prosecution is not necessarily obstruction of justice. Prosecutors too must live by the rules.

There is no justice to obstruct in a malicious prosecution.

Stephen B. Young is a former assistant dean at Harvard Law School and former dean of Hamline University School of Law. In 1974, he researched constitutional history for John Doar, special counsel to the House Judiciary Committee on articles of impeachment against President Richard Nixon.