OPINION — It was the most important midterm election since voters repudiated the unsteady hand of Herbert Hoover in responding to the Great Depression. But unlike 1930 when the Democrats garnered more than 50 House seats and gained effective control of the Senate, the electoral verdict last night was far more equivocal.

As anyone who spent last summer at the beach knows, waves come in all sizes. There are gentle waves made for diving seven-year-olds. There are deceptively strong waves that bring with them an undertow. And there are, of course, fierce storm waves that require a response from FEMA.

Republicans, from Donald Trump on down, will dismiss last night’s Democratic victories as a wave worthy of a kiddie pool. Already, the early-rising Trump tweeted about “our Big Victory last night.” And, in terms of the Senate where at least three and maybe five Democratic incumbents lost, there is a rationale to the Trumpian hyperbole.

Received so many Congratulations from so many on our Big Victory last night, including from foreign nations (friends) that were waiting me out, and hoping, on Trade Deals. Now we can all get back to work and get things done!

— Donald J. Trump (@realDonaldTrump) November 7, 2018

But, in truth, the 2018 midterms appear to have brought with them a lasting Democratic undertow.

Looking at the House map from Portland, Maine, to the North Carolina border, only by squinting do you see occasional small splotches of red in places like Long Island. Across the board, Republicans had problems in upmarket, mostly white, congressional districts from Charleston, South Carolina, to Oklahoma City.

The new Democratic House majority — and the almost certain return of Nancy Pelosi as speaker — represents a triumph over gerrymandering. Not too long ago political orthodoxy decreed that the Republicans would control the House until after the 2020 Census because the district lines were so artfully drawn by the GOP after the Democratic wipeout in the 2010 elections.

Instead, the 2018 House elections were a belated vindication of Hillary Clinton’s failed 2016 strategy of pitching herself to college-educated suburban Republican women. These women were Clinton’s target audience when she maladroitly described half of Trump supporters as “a basket of deplorables” because of their “racist, sexist, homophobic, xenophobic” views.

As Trump in the White House fulfills every dire prophecy about his vitriolic fear mongering, affluent suburbs are increasingly becoming part of the permanent Democratic coalition. Republican incumbents who survived 2018 in districts like Ohio-12 (the Columbus suburbs) and Pennsylvania-1 (Philadelphia suburbs) have reason to be fearful of increased Democratic turnout in the presidential year of 2020.

Trump also tweeted on Wednesday morning “To any of the pundits or talking heads that do not give us proper credit for this great Midterm Election, just remember two words – FAKE NEWS!”

As a pundit fearful of the ire of a press critic like Trump, I will happily give him proper credit for losing the House.

To any of the pundits or talking heads that do not give us proper credit for this great Midterm Election, just remember two words – FAKE NEWS!

— Donald J. Trump (@realDonaldTrump) November 7, 2018

The Democrats faced the most daunting Senate map in memory with only nine GOP-held seats on the ballot. Trump responded with fact-free rallies designed to stoke fear of a dwindling caravan of desperate asylum-seekers hundreds of miles from the U.S. border. And it worked in states like North Dakota, Indiana and Missouri — none of which will be in play in the 2020 presidential election.

That said, Democrats still face a moment of reckoning in understanding Trump’s continuing appeal. The president’s support level a bit above the 40 percent mark remains impervious to anything less than nuclear weapons. In fact, the Democrats’ apparent 8- to 9-point edge in the national House vote lines up neatly with Trump’s approval ratings.

A national rebellion against Trump might have elected matinee-idol candidates like Beto O’Rourke in the Texas Senate race and Andrew Gillum in Florida’s gubernatorial contest. But demographic change in politics often comes more slowly than the fantasies of hopeful partisans.

When the 116th Congress convenes in January, no one should waste too much time analyzing potential legislation. With a House majority, the Democrats have the power to block any further assaults on Obamacare. But it seems fanciful to believe that a divided Congress will produce anything beyond maintaining the basic housekeeping functions of government.

Since, unlike the Trump-era Republicans, the Democrats remain a big-tent party, Pelosi in normal times might have problems managing her small House majority. But what matters in the new House will be committee chairmanships and subpoena powers rather than floor votes. And when it comes to organizing the House, even a single-vote margin is sufficient.

It is impossible to know whether vigorous investigations of the Trump regime will pay political dividends to the Democrats. But after two years of supine Republican see-no-evil under-sight of the government, the Democrats’ ability to deploy the power to probe will restore Congress’ constitutional role as an independent branch of government.

With an enhanced Senate majority, Mitch McConnell will have even greater latitude to reshape the federal judiciary with conservative jurists. In fact, by 2020, any member of the right-wing Federalist Society who is not a federal judge will have ample grounds to be embarrassed for being passed over.

At some point, though, those Republicans with a sense of decency and a belief in truth-telling will have to look in the mirror and contemplate the costs of being a Trump congressional enabler. Nothing about the 2018 election should give Republicans the confidence that marching in lockstep with Trump puts them on the right side of history.

But for the moment, the Democrats are entitled to a deep sigh of relief. While it was not an Election Night of candy canes and elves prancing on the Capitol lawn, it was good enough to constrain Donald Trump. And that alone made it the most important midterm since 1930.

Walter Shapiro has covered the last 10 presidential campaigns. He is also a fellow at the Brennan Center for Justice at NYU and a lecturer in political science at Yale. Follow him on Twitter @MrWalterShapiro.