It was ghoulishly fitting that Donald Trump got out the long knives on the Ides of March. On a day when top Trump officials might have been justifiably nervous about going to the Forum, Trump apparently decided to fire national security advisor H.R. McMaster, according to The Washington Post.

If McMaster has indeed joined Rex Tillerson in the ever-growing Trump Alumni Association, it should put to rest the glib theory that the so-called “adults in the room” could constrain a petulant president.

Under Trump, the only quality that matters is sycophancy. The president could be surrounded by a Wailing Wall of dissenters and still ignore their advice based on gut instinct or a fragment that he half remembered from “Fox and Friends.”

Luckily for American democracy, the Founding Fathers came up with an idea for checking the power of an imperial president. It was a separate institution they called Congress and, in theory, it has broad powers when it comes to the budget, foreign military adventures and oversight of the executive branch of government.

Invertebrate institution

But James Madison and Company never anticipated a Congress as supine as the current House and Senate under Republican control.

In the 1970s, Congress was more upset about the penny-ante antics of Billy Carter (Jimmy Carter’s scapegrace brother) than this Congress is about Jared Kushner and Ivanka Trump promoting their personal businesses and conducting high-stakes deals (real estate sales, licensing agreements) while supposedly serving on the White House staff.

A bedrock principle of the Republican Party for decades has been free trade. Yet when Trump slapped tariffs on steel and aluminum using a dubious national security justification, there were murmurs of protest by individual congressional Republicans, but an abject refusal by the GOP leadership to challenge the president.

As a timorous Mitch McConnelltold reporters this week, “On the trade issue, as all of you know, the administration pretty much has ball control. The thought that the president would sign a bill that would undo actions he’s taken strikes me as remote at best.”

Principles have been abandoned over the years by both parties for short-term political advantage. But as Democratic triumphs in both Alabama and PA-18 have dramatically illustrated, the Republicans are doing themselves no favors with their Faustian bargain with a president who believes in nothing outside of himself.

Matthew Dowd, a top strategist in George W. Bush’s presidential campaigns, has long argued that congressional Republicans should challenge “the president when he is out of step with the country and hold him accountable for his words and actions which divide the country.” Instead, as Dowd stressed in a column for ABC News after Tuesday’s special election, “The GOP has done the exact opposite of this strategy, enabling President Trump each day. And the GOP has underperformed or lost nearly every race held.”

In short, not much is left when a party abandons both principle and prudent politics.

And midterm hope?

The weather forecast from the special elections and most polls on congressional preference suggests that skies of Democratic blue will cover the political landscape in November. At stake in this year’s congressional elections are matters far larger than partisan advantage or the fate of the president’s legislative agenda.

Yes, every congressional election is packaged as the electoral equivalent of Armageddon. But years of hyperbole over threats to Social Security and hunting rifles should not deaden us to the reality that 2018 is more significant than any off-year congressional election in the past century.

Watch: Pelosi: Lamb Win in Republican District a ‘Tremendous Victory’

Granted, there are other contenders.

The short-lived Newt Gingrich revolution of 1994 ended a four-decade Democratic stranglehold on House majorities. The Republican sweep in the 1946 elections effectively ended the New Deal and brought a generation of rabid anti-communists like Joseph McCarthy to power. And the 1930 Democratic landslide conveyed the force of voter rage at Herbert Hoover for the Depression.

But in none of these elections were the bipartisan norms of American democracy on the ballot. The closest analogy might have been 1974, had Richard Nixon still been clinging to power rather having resigned that August.

Please understand: I am not claiming that impeachment is or should be on the ballot in 2018. Just because a liberal legal icon says the words “obstruction of justice” on MSNBC does not bring us any closer to a bipartisan consensus (as occurred with Nixon) that the president should be removed from office.

A Democratic takeover of the House and a split verdict in the Senate would probably not even produce much anti-Trump legislation. The combination of the Senate filibuster and the president’s veto power limits the chances for laws that constrain the president’s impetuous conduct.

But a Democratic House would eliminate the most embarrassing blot on the record of this Republican Congress — a stunning lack of curiosity about how Trump is running and ruining the executive branch.

Congressional committees armed with subpoena power should be following up on news stories suggesting a consistent pattern of self-enrichment by the Trump family. There should be more than a sputtering interest in the squandering of money by self-important Trump appointees, from Ben Carson’s $31,000 executive dining room to Steven Mnuchin’s $1 million in travel costs on military planes.

Pay to play

Many Americans live paycheck to paycheck. Donald Trump lives payback to payback.

As a result, there is much we do not know about the pressures that the president has put on the Justice Department to investigate Hillary Clinton. And has anyone checked to see if the IRS has been asked — in Nixonian style — to target Trump’s enemies?

There should also be bipartisan concern over the flight from competence in the Trump administration. The combination of the exodus of respected career officials and the arrival of junior Trump acolytes has hollowed out the government from the EPA to the State Department.

Congress cannot go on ignoring Trump’s reign of error as if it were occurring in an alternate universe. The stakes for democracy and America’s role in the world are too high for Congress to continue to shout, “It’s not my table.”

Oversight of an alarming president — who appears to be throwing off all restraints — is what is on the ballot this November. And that is why 2018 has become the most important off-year election in more than a century.

Roll Call columnist Walter Shapiro is a veteran of Politics Daily, USA Today, Time, Newsweek and The Washington Post. Follow him on Twitter @MrWalterShapiro.