WASHINGTON — The obvious unifying element for Democrats looking ahead to the 2020 presidential election is their imperative to oust Donald Trump from the Oval Office. They desire it for a multitude of reasons, starting with his glaring incompetence for the job and the rampant corruption in his regime.

But if the campaign comes off as only a bitter vendetta against Trump, it will fail to identify the deep damage he has already inflicted on our constitutional brand of self-government with his autocratic ways.

His war on Congress in conflict with America’s separation of powers among our co-equal executive, legislative and judicial branches is a direct and brutal assault on our small-“d” democratic system.

His blatantly illegal usurpation of the congressional power of the purse — raising and authorizing public money to run the country, including its vital military arm — should itself be an impeachable offense.

So should Trump’s direction to administration officials to ignore congressional subpoenas for testimony dealing with his various governmental and private-business activities. It first laughs off foreign intervention in our elections process and then skirts emolument prohibitions expressly barred in the Constitution.

In all this, the Trump presidency is an open attack on our cherished political principles across the board, for more than two years eroding and defiling them to the detriment of our standing on the world stage.

At home as well, Trump has shattered one of our two great political parties, leaving the GOP a shell of its former conservative stronghold. It is populated by an army of compliant toadies on Capitol Hill who have stood by while traditional Republican values have been run roughshod in Trump’s insatiable demand for worship of self.

Whether Trump is defeated in the election, impeached and removed, or escapes unpunished, the Grand Old Party is unlikely ever to be the same again, nor the two-party system itself for that matter.

The dominant Republican figure in the Senate, Majority Leader Mitch McConnell of Kentucky, marches in obedient lockstep with the arrogant president. McConnell stands resolutely barring the door to impeachment in the Senate if the House Democrats were to convict Trump of obstruction — unlikely right now.

A solitary breach in the congressional wall of compliance to Trump came last week in the resignation from the party of a former member of its ultrconservative Freedom Caucus in the House, Rep. Justin Amash of Michigan. He left with a hint of challenging the president as an independent in the 2020 election and with a blast at both parties, writing in the Washington Post:

“The two-party system has evolved into an existential threat to American principles and institutions. Instead of acting as an independent branch of government and serving as a check on the executive branch, congressional leaders of both parties expect the House and Senate to act in obedience or opposition to the president and their colleagues on a partisan basis.”

Amash, in his fifth House term, went on to castigate both parties for the impasse: “We are fast approaching the point, however, where Congress exists as little more than a formality to legitimize outcomes dictated by the president, the speaker of the House and the Senate majority leader.”

Trump promptly and characteristically tweeted back: “Great news for the Republican Party as one of the dumbest and most disloyal men in Congress is quitting the party. No Collusion, No Obstruction! Knew he couldn’t get the nomination to run again in the Great State of Michigan. Already being challenged for his seat. A total loser!”

Such is the state of turmoil within the party of Lincoln, Teddy Roosevelt, Eisenhower and now Trump. At the same time, the opposition party ponders whether getting rid of Trump must be its primary goal, or should it be what ideological direction the party takes if or when Trump is gone.

The Democrats, in concentrating now on who should lead them in 2020, may risk hampering their first imperative task for the country’s sake, of seeing that it won’t be Donald Trump for another four years.

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 juleswitcovercomcast.net.

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