A key to President Trump’s apparent escape from the clutches of Special Counsel Robert Mueller’s investigation was his simple refusal to testify under oath. He thereby dodged the “perjury trap” his lawyers warned about.

Consequently, although Trump lied daily like a trooper on all manner of important issues, he never did so with his hand raised. His current personal lawyer, former New York Mayor Rudy Giuliani, endured endless press ridicule as a laughable bumbler. But in the end he saved his client from political suicide, at least through the two-year duration of the Mueller inquiry.

The contents of Mueller’s report have not been made public. But on Sunday Attorney General William Barr released a letter to the House and Senate judiciary committees summarizing what he called Mueller’s “principal conclusions.” Barr quoted the report stating that “the investigation did not establish that members of the Trump Campaign conspired or coordinated with the Russian government in its election interference activities.”

With respect to obstruction of justice, Barr quoted the Mueller report as follows: “while this report does not conclude that the President committed a crim, it also does not exonerate him.”

The practical effect should be to kick the issue to the House of Representatives, which constitutionally is empowered to initiate any impeachment of the president, followed by a trial in the Senate, which can convict with a two-thirds majority vote.

In plain terms, strict constitutionalist Mueller adhered to the role of Congress in impeachment, under which no president has ever been found guilty. The two who were impeached by the House, Andrew Johnson in 1868 and Bill Clinton in 1998, were acquitted, in Johnson’s case by a single vote.

Watergate sleuth Bob Woodward noted last year in “Fear: Trump in the White House,” that John Dowd, then Trump’s lawyer, “remained convinced that Mueller never had a Russian case. He was looking for a perjury trap. And in a brutally honest self-evaluation, he believed that Mueller had played him, and the president, for suckers in order to get their cooperation on witnesses and documents.” Giuliani merely bought into the same waiting game when he joined the Trump legal defense team.

In the Watergate scandal 45 years ago, it was widely argued, correctly, that the American system of justice had worked, with the forced resignation of Richard Nixon in the face of irrefutable evidence of a “smoking gun.” His taped words ordering the CIA to lay off on the Democratic National Committee break-in, and Nixon’s talk of raising hush money for the burglars, sealed his doom.

Then, the Supreme Court settled Nixon’s hash by requiring release to Congress of the incriminating tapes, persuading Nixon’s friends Sen. Barry Goldwater and Rep. John Rhodes to tell him to his face that the jig was up.

This time around, getting Trump to throw in the towel will not be so easy. It could come to Senate Republicans convincing him he lacks the votes to save his skin in an impeachment process. Or the Supreme Court may rule a sitting president can be indicted after all. Neither seems likely now.

At least three House committees with subpoena power are poised to pick up the responsibilities of investigating Trump and his associates, while Justice Department sleuths look into potential financial crimes associated with the Trump Organization in other courts.

But don’t expect Donald Trump to give up and fly off to Mar-a-Lago the way Nixon retreated to his own hideaway at San Clemente. That would be totally out of character for this president, especially now that he has more basis than before in claiming there has been “no collusion” with Russia or anybody else.

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Jules Witcover’s latest book is

“The American Vice Presidency: From Irrelevance to Power,” published by Smithsonian Books.