WASHINGTON — The Republican Party once was acclaimed as the staunch defender of law and order by the likes of Richard Nixon, Barry Goldwater and Ronald Reagan. But now it finds itself engaged in a civil war over Donald Trump’s Justice Department and the FBI.

The dichotomy is demonstrated in the much-ballyhooed Nunes memo, written at the instruction of Rep. Devin Nunes, the California Republican who chairs the House Intelligence Committee, or possibly by someone in the Trump administration. Nunes made a recent late-night journey to the White House and returned with the makings of the mysterious missive that now roils Congress.

The memo professes to establish, among other things, that FBI staff members were out to sabotage President Trump, were engaged in nefarious conduct as part of some sort of deep-state monkey business.

The president has seized on the Nunes memo, after authorizing its publication, as “total vindication” of allegations that he or aides had colluded with the Russians in the 2016 election that handed him the presidency.

Democrats on the committee, led by ranking member Adam Schiff of California, have assailed the memo as incorrect and/or doctored, complaining that a version of their own has been denied the light of day by Nunes and now by Trump. Sideliners with no skin in the game have called for release of the Democratic version as well, but so far to no avail.

What is bizarre as well as suspicious about the whole affair is that the Republican president has taken issue with top Justice Department and FBI officials he himself appointed. They warned him in advance that publication of the memo would recklessly impair their work in the investigation and the agencies’ ability to do their jobs.

Does “obstruction of justice” begin to ring a bell here? That allegation of course is at the heart of the inquiry. If taken to its political conclusion, that charge would open the way for the impeachment and trial of the president.

Trump’s repeated excoriations of the Russian meddling investigations as a “witch hunt” or “hoax” aimed squarely at him invites comparisons with the experience and failed defense of Nixon in 1972-74 in the Watergate scandal.

Nixon forced the resignations of his two top Justice Department officials, Attorney General Elliot Richardson and Deputy Attorney General William Ruckelshaus, for declining to fire special prosecutor Archibald Cox as the noose began to tighten on the 37th president.

Trump, after firing FBI Director James Comey and subsequently hinting he might do the same to Special Counsel Robert Mueller and Deputy Attorney General Rod Rosenstein, has backed off those threats through a White House press spokesman, for now at least. One might think that Nixon’s experience would lead Trump to choose some other way to call off the judicial dogs.

Nixon chose to resign rather than to face impeachment when old Senate friends like Goldwater confronted him with the cold fact that he lacked the votes to defeat it. This time around, the Republican congressional leaders, House Speaker Paul Ryan and Senate Majority Leader Mitch McConnell, are now marching in lockstep behind Trump after earlier reservations about his comportment.

By his stubborn temperament, and in his extreme self-assurance that the GOP will stand firmly behind him no matter what comes, Donald Trump is likely to dig in his heels and strive once again to beat whatever odds the political handicappers place against him.

From now until the November midterm elections, those tests loom as the critical battleground as Trump defends himself against his own Justice Department and FBI. His best bet now is that the thriving economy, despite recent stock market plunges, and new tax cuts will in the end carry the day for him, along with the pied piper magic he exerts on his true believers.

Jules Witcover can be contacted at juleswitcover@comcast.net.