WASHINGTON — As Donald Trump brazenly attempts to rob Congress of its constitutional power of the purse, he seeks to divert public attention by assailing the large field of 2020 Democratic presidential candidates.

He is eager to turn the run-up to the next national election into a premature campaign brawl, rather than what’s needed now — a public defense of America’s democratic principles and mechanisms.

His obvious strategy for re-election next year is to detour from his various political woes, be they Justice Department and congressional investigations or just personal behavioral lapses. He’d prefer focusing on the real or alleged shortcomings of the Democrats seeking to oust him from the Oval Office.

The news media, slandered by Trump as “the enemy of the people” in his campaign to muddy the waters of legitimate journalistic inquiries, have in some instances cooperated by sinking to ludicrous lows, spreading frivolous allegations unworthy of a presidential campaign.

Incredibly, the longshot candidacy of Sen. Amy Klobuchar of Minnesota has drawn headlines from a report that she was caught eating a salad with her hair comb when she lacked a proper fork, and then asked a staff worker to clean it for her.

This supposed lapse in etiquette if not cleanliness has been cited as grounds to bar her from the presidency. Such a social faux pas apparently would negate her reputation as a paragon of “Minnesota nice.”

The illustration is a laughable example of the press and/or social media cutting a White House aspirant down to size for a bizarre triviality. But as Finley Peter Dunne’s Mister Dooley famously said, “Politics ain’t beanbag.” So an anything-goes attitude may prevail amid the handicappers at the rail of the next presidential horserace, unless they become more discriminating in what they report as newsworthy.

In this context, Donald Trump has tipped his hand with his early inclination to turn his expected bid for a second term into a muddy professional wrestling match against anyone who challenges him. Rather than getting into the gutter with him, the Democrats and other Republicans as well need to take the high road.

One old GOP establishment figure of some stature, former two-term Massachusetts Gov. Bill Weld, has returned to the party fold after serving as running mate to 2016 Libertarian presidential candidate Gary Johnson, challenging Trump as a defender of the Constitution. Weld is likely to get nowhere except to give other old establishment Republicans a vehicle for expressing their disgust with their party’s chaotic bully.

More significant may be the 16 state attorneys general who have filed suits in lower federal and/or state courts against the president’s national emergency order stealing Congress’s power to appropriate federal spending.

The judicial pushback indicates that this time the reckless president has grabbed a judicial tiger by the tail. All 16 state law-enforcement officials, not surprisingly, are Democrats.

Their joint suit, filed in the Federal District Court in San Francisco by California Attorney General Xavier Becerra, charges: “Contrary to the will of Congress, the president has used his pretext of an artificial ‘crisis’ of unlawful immigration to declare a national emergency, redirecting federal dollars appropriated for drug interdiction, military construction and law-enforcement initiatives toward building a wall on the United States-Mexican border.”

Never has Trump’s failure to pay attention to White House and Cabinet aides who may have cautioned him against self-inflicted wounds been better illustrated.

This fiasco offers a golden opportunity for Republicans in Congress, be they old establishment standbys cowed by Trump up to now or the GOP members who survived the Democratic blue wave of last November, to reassert a voice in their hijacked party.

As for the declared Democratic hopefuls, they are vowing to accent the positive in their progressive agendas, leaving the mud-slinging to the master of it.

But in light of the expectation that the 2020 race will be first and foremost a referendum on the incumbent, the odds are very slight that it will be waged under a political version of Marquis of Queensberry rules.

Editor’s note: Jules Witcover’s latest book is “The American Vice Presidency: From Irrelevance to Power,” published by Smithsonian Books. You can respond to this column at juleswitcover@comcast.net.