Read this before you buy the ‘blue tsunami’ hype

The news is awash these days with poll-inspired expectations about Democrats winning big in next month’s midterm elections . USA Today declared the other day that “the expected blue wave could be even bigger than expected, and could not only give Democrats control of the House, but also the Senate.” Even more expansively, Huffington Post proclaimed : “Historic victories are seemingly within grasp” for Democrats.

And yet, solid reasons exist for treating such poll-based narratives cautiously, even warily, given that surveys are inherently fragile instruments for measuring an ephemeral electorate. As data journalist Nate Silver has noted , “It’s not unreasonable to approach election polls from a position of mild — maybe even more-than-mild — skepticism.”

This is not to say poll-driven expectations are bound for error . They might be accurate; the Democrats might enjoy a “ blue tsunami ” of electoral success next month.

But there are compelling reasons for tempering pre-election headiness — reasons that are rooted in polling’s checkered past. The following summary of recent shortcomings in election polling offers context and justification for tapping the brakes about poll-driven high hopes this year.

Election polls have been underestimating Republicans

Pollsters in 2024 underestimated Donald Trump’s popular support for the third successive presidential election . His vote totals increased in each of the three races, from almost 63 million in 2016 to about 74 million in 2020 to more than 77.3 million in 2024.

Of course, Trump is not on the ballot in 2026, but he has encouraged midterm voters to “close their eyes and pretend” that he is, symbolically.

The hypothesis is that Trump’s presence on the ballot attracts participation by Republicans who otherwise might not vote. But the problem of underestimating Republican turnout goes beyond the Trump candidacies.

More broadly, polls collectively have overstated support for Democratic candidates in five of the past six national elections, according to data posted by Scott Clement, polling director for The Washington Post. If the midterm polls this year systematically overestimate support for Democratic candidates by an average of 3 percentage points, Clement wrote, Democrats likely will win the House but fail to gain control of the Senate.

Pollsters with exceptional records for accuracy have still been known to err dramatically. Reputation brings no insulation from polling embarrassment . This reality has been apparent since the presidential election of 1936 , when Literary Digest magazine — the acknowledged polling oracle of its day — predicted Republican Alf Landon would easily defeat President Franklin D. Roosevelt. The Digest’s projection was based on its huge mail-in poll, which understated Roosevelt’s popular support by nearly 20 percentage points. Landon lost in a landslide, carrying just two states.

More recently, J. Ann Selzer, whose previously stellar survey work won for her acclamation as the “ queen of polling ” and “ best pollster in politics ,” erred dramatically in 2024. Her final Iowa poll before the presidential election said Democrat Kamala Harris had “ clearly leaped into a leading position ” and was 3 points ahead of Trump in the Hawkeye State. The poll result was as stunning as it was unexpected . All but overlooked in the frenzy were results of a concurrent survey by Emerson College that showed Trump leading in Iowa by 10 percentage points.

In the end, Trump carried the state by 13 points , which meant Selzer’s poll was off by 16 points. Soon afterward, Selzer made known her plans to quit election polling. “Polling is a science of estimation,” she said , “and science has a way of periodically humbling the scientist.”

Election polls commissioned or conducted by major news organizations unsurprisingly attract wide attention. The results are promptly shared with large audiences of viewers and readers. But for all their prominence, media polls can be problematic.

In 2024, swing-state polling late in the campaign by CNN, The New York Times/Siena College , and Marist College for PBS and NPR all had Harris leading in enough swing states to win the Electoral College. Had those media polls aligned with election outcomes in swing states, Harris would have been elected president.

Trump carried all seven swing states, if by narrow margins in some of them.

CNN and the Times/Siena poll estimated the race nationally was tied at campaign’s end. Marist estimated that Harris led nationally by 4 points . Trump won the national popular vote by 1.5 points .

The midterm elections four years ago were expected to produce a “ red wave ” of Republican gains in Congress. The political landscape looked bleak for Democrats in the fall of 2022. Inflation was raging then at 7.7 percent , unlawful cross-border migration was surging , and President Biden’s approval rating was down to 40 percent.

The red wave never materialized . Democrats scored a net gain of one Senate seat and kept control of the upper chamber. Republicans picked up just nine seats in the House , enough to give them a wobbly majority.

The better-than-expected outcome for Democrats contributed to Biden’s ill-fated decision to seek reelection in 2024. Biden won all the Democratic presidential primaries that year but quit the campaign in July 2024 following a disastrous debate against Trump.

Polls overall missed the margins of victory by 4 percentage points or more in key Senate races in Arizona, Colorado, Florida, New Hampshire, Pennsylvania and Washington. In New Hampshire, Democrat Maggie Hassan exceeded the RealClearPolitics polling average by nearly 8 points . In Washington state, Democratic Sen. Patty Murray outperformed the polls by 11 points.

None of this, of course, is to say that election polling’s flawed past is necessarily prologue. But it is reasonable to be braced for surprises, as polls might not offer an accurate indication about elections outcomes.

As the late polling innovator Warren Mitofsky once said about placing excessive confidence in survey data, “There’s a lot of room for humility in polling. Every time you get cocky, you lose.”

W. Joseph Campbell is a professor emeritus at American University in Washington, D.C. His seven solo-authored books include “ Lost in a Gallup: Polling Failure in U.S. Presidential Elections .”