Is a “blue wave” really coming to sweep Republicans out of office?

For a while, it seemed Democrats were poised for a historic election that would bring them back into power in one or both chambers of Congress.

At one point last December, a CNN/SSRS poll gave Democrats a whopping 18-point advantage in the generic ballot. (Polls like this ask voters if they are likely to pick a Democrat or Republican for Congress.) As the Times pointed out, a 13-point advantage would be comparable to or larger than the one Democrats had when they retook the House and Senate in 2006.

Other factors seemed to suggest that things were moving in Democrats’ favor. A record number of House Republicans — including Speaker Paul Ryan — have announced their decisions to retire in lieu of facing battles for reelection.

But with midterm primaries underway, some of that early momentum appears to be flagging. In light of booming economic growth, Republicans are starting to make some inroads of their own, including narrowing voter margins on the generic ballot and a steady rise in President Donald Trump’s approval ratings. The electoral math on a number of crucial districts is also beginning to look tougher for vulnerable Democrats, with relatively safe states like Florida and Ohio emerging as possible battlegrounds.

“The blue wave may not be crashing, but its seeming inevitable ascendancy has certainly flattened out,” says Tim Malloy, an assistant director of the Quinnipiac University Poll. “Our surveys show the president’s numbers rising, gradually building on a surging economy.”

I talked to 11 experts to get their take on the likelihood of a blue wave actually coming to fruition. Here’s what I learned.

The data has changed for the Democrats — but it could still go either way

Patrick Murray, director of the Monmouth University Polling Institute, says the influx of recent data has, indeed, tempered the Democratic lead in the generic ballot. He emphasized, however, that a lot more information was likely to continue affecting the polls in the months to come until Election Day.

“Let’s pour a little water on the hot takes,” he said. “The generic House ballot seems to have improved for the Republicans … although this average is driven largely by a few polls that have been bouncing around a lot.”

Murray says this variability is what makes it tough to make any sort of definitive call at this point in the race. “In reality, the generic ballot has been pretty stable since March but is significantly worse for Democrats than where it was at the start of the year,” he said. “The Democrats are not in the same enviable position they were five months ago, but that doesn’t mean we have any idea what the next five months will bring.”

Jay Leve, the president of SurveyUSA, noted that it was important to take such polling measures day by day. “It’s ebb tide for the Democrats right now. That may change any moment, but if [there’s] a general election today, there is no blue wave,” he said when asked earlier this week.

MIT political science professor Charles Stewart, who specializes in the study of election data, argues that the odds have always been roughly 50-50 for Democrats to retake the House — and even slimmer for them to flip the Senate. He doesn’t think this has changed much since the 2016 election.

“The case that the wave was never as big as the Democrats hoped is based on two things,” he said. “First, to capture the House, Democrats would have to see the biggest election swing [from presidential election to the next midterm election] in their favor in the entire post-World War II era. And, even then, they would only have a 50-50 chance of taking the House.”

There are lots of countervailing forces at play

Historically, the pendulum tends to swing back against the president’s party during midterm elections. Democrats, however, hold seats that are harder to defend, especially in the Senate. In both chambers, there’s also the push and pull of factors like negative Trump sentiment bolstering Democrats’ chances, while the strength of the economy bodes well for Republicans.

The presence of these countervailing forces can serve to muddle attempts at predictions, especially when the actions of an individual candidate are yet another unknown thrown into the mix.

“When looking at the fate of the Senate, we’re seeing a collision of two big factors — a historical trend of the president’s party losing seats versus an electoral map that highly favors the Republicans,” says University of Houston political science professor Elizabeth Simas. “In these races, the quality of the candidates and their campaigns are going to be very important. Republican candidate blunders certainly helped both Joe Donnelly (D-IN) and Claire McCaskill (D-MO) in 2012.”

Candidate blunders are among the variables that Vox’s Dylan Scott has previously highlighted when detailing the myriad things that could still change — and shape the election — in the months to come.

“It is entirely possible that events might occur between now and November that could shift the momentum to the Republicans or, alternatively, lead to the Democrats taking control of Congress,” says USC law professor Franita Tolson. “Any predictions that are made about the blue wave crashing, based on polling about the economy conducted five months before the elections, are premature.”

“Ultimately, I think trying to make accurate predictions at this point is a little like trying to pick a World Series champion in April,” says Simas.

Democrats will likely see gains — but it’s unclear how much

While it may be way too soon to determine which way the midterms will definitively go, experts say it’s likely fair to say that Democrats will see some pickups. What’s unclear is whether this will be a true wave or just a steady drip.

“Democrats are sure to make gains in this year’s midterm elections, but the monstrous wave that appeared to be building in late 2017 now appears to be more modest,” says Barry Burden, a political science professor at the University of Wisconsin Madison.

As Vox’s Matt Yglesias writes, despite the declines in Democrats’ generic ballot numbers, the data, including the results of the California primary, still hints at a likely advantage for the party:

Though it feels like the odds for liberals have gone from overwhelmingly positive to desperate quickly, the reality is a bit duller. As a country we have, in many ways, failed to process some of the key lessons of the 2016 campaign. Modest-sized polling errors are common, events are important to politics and they are inherently unpredictable. But Democrats retain an edge in the polls, and the results from California continue to suggest that Democrats are modest favorites to win a House majority.

MIT’s Stewart also argues that the progress Republicans have made this year couldn’t make up for the lingering and pervasive negative impact of Trump’s unpopular presidency. “Even if Trump’s popularity is easing up and the economy continues to be strong, the damage has already been done,” he says. “The question remains, how bad will the damage be to the Republicans in the House?”

Much will come down to voter turnout and winning over independents

“If there is going to be any kind of wave, it’s going to require a strong turnout from Democratic voters,” says Simas. It’s a lesson Democrats learned in 2016 when voter turnout ended up being a major Achilles’ heel. At the time, Reuters polling director Julia Clark told Vox, “When fewer people vote, Republicans do better. That’s a modern political fact.”

Emerson’s Spencer Kimball notes that voter registration could be an important indicator to track as a sign of engagement ahead of the election. “Florida, for example, has seen a slight pickup in GOP voters and a slight downtick in Democratic voters,” he says. “This may be an indication of under-the-radar momentum, similar to voter shifts in Pennsylvania in the 2016 primaries.”

In California, meanwhile, the state saw voter registration numbers for independents surpass those of Republicans for the first time last week.

Much like in the 2016 presidential election, independents will be particularly important to watch, says Harvard Kennedy School’s Pippa Norris, who pointed to a May YouGov/Reuters survey that highlighted a general uncertainty among independents about which party to go with.

“Trump appeals strongly to the base, but he hasn’t reached beyond to independents, the largest category in the electorate. These are also the people most up for grabs — and least likely to vote,” she adds. “So any appeal by either party has to reach the independents, which means the center of the political spectrum, not the conservative or liberal wings.”

“Competing for independent women and married women will be key to the margin of victory,” Democratic pollster Celinda Lake says, adding that she perceives Democratic voters to be “more motivated than Republicans and more consolidated.”

In an interview with Bloomberg, Peter Hart, who conducts the Wall Street Journal/NBC News poll, also cited voter “intensity” as a factor Democrats have going for them: “Two-thirds of Democrats in [the] survey expressed a strong interest in this year’s election versus 49 percent of Republicans, exactly the intensity advantage Republicans had in 2010, when they won back the House in a landslide.”

Tufts political science professor Eitan Hersh was a bit more wary about the electorate’s broader energy ultimately translating to a desired result for Democrats. “Democrats should indeed worry about complacency,” he said. “On the left, there was a sense in 2016 that Trump was so toxic of a candidate that Clinton’s victory was inevitable. So Democrats voted less and volunteered less than they otherwise would have.”