As the 2018 midterms draw closer, President Trump continues to claim there is a "Red Wave!" brewing.The problem is that concrete voting data shows a very different type of wave forming — one that's poised to give Democrats a comfortable majority in the House.Republicans may hold onto eight of the nine GOP-held seats in special congressional elections on the ballot since 2016 (one is still officially undecided), but the massive voter shift toward Democrats in what should be comfortably red territory shows plenty of warning signs for Republicans this fall.The open seats were in overwhelmingly Republican areas, places Trump carried by upwards of 20 points in most cases. But Democrats were able to narrow most of those races to single-digit losses.Based on calculations by NPR, the average special election shift was 10 points toward the Democrats. If you apply that margin to all 435 congressional districts — using the 2016 presidential margins as a partisan baseline — the Democrats would net 63 seats. That's certainly on trend for a blue — not red — wave and for far more than the 23 seats they need to flip the House.Even if Republicans were to match their best performance in a recent special election, it would be an eight-point shift toward the GOP, netting them 16 seats. That might be more of a red low tide, but one that Republicans would certainly be ecstatic with, given that they would keep control of the House.If we apply the same criteria in the other direction, looking at the best performance by a Democrat, we're not just talking about a blue wave anymore – it's a tsunami. Democrats' best performance in a special election cycle was 21 points over the presidential margin there. Such a scenario would give Democrats a 129-seat pickup. That would be the largest party shift in modern history, and such a hypothetical remains highly unlikely.Both parties caution that special elections are, by their very nature, distinct and, well, special. And they aren't perfect predictors of what might happen in November, with outside factors and often candidate quality shaping outcomes.But what this year's elections have shown — and what GOP and Democratic strategists agree on — is that Democrats have a massive enthusiasm edge, while Republicans are having trouble motivating their voters.Democrats say that, yes, they would have liked to have more "W"s on their side over this past year and a half, but the data shows that trends are moving heavily in their favor when it matters most — Election Day. They have had other tangible victories — the Virginia and New Jersey 2017 gubernatorial contests, and 43 state legislative seats that flipped from red to blue since Trump took office."If we're looking at these special elections for trends or clues to November, Democratic turnout is better than Republicans', and Democrats are doing better than Republicans in suburbs," said Democratic pollster Fred Yang.And while Trump and his supporters may discard polls as "fake news" or "rigged," because many didn't predict the president's own victory over Hillary Clinton in 2016, this very real voting data shows a much grimmer reality for Republicans — but one that they know is coming and are trying to prepare for as best they can."I do think special elections in general are not always the best predictor of what we're going to see in the fall. However, when you look at all of the special elections from this past year, it's not really a new phenomenon," said GOP pollster Robert Blizzard. "Democrats are still highly energized, while Republicans are just more complacent right now than they have been in previous cycles."Blizzard was the pollster for Republican Troy Balderson's campaign in Ohio's 12th District earlier this month. Balderson is clinging to a narrow 1,564-vote lead over Democrat Danny O'Connor as both parties await provisional ballots to be counted, and The Associated Press has not yet called the race. But even if Balderson's lead does hold, Blizzard acknowledged there were still warning signs for Republicans, especially in suburban areas, and in holding open seats like this one. There are about 70 districts more friendly to Democrats than the Ohio one — meaning they don't even need seats like that one to get to a majority.In the suburban Columbus counties, Democrat Danny O'Connor overperformed 2016 benchmarks, but Balderson was able to make up the difference by driving up margins in the more rural areas, buoyed by a visit from President Trump and an endorsement from Ohio Gov. John Kasich — two men who represent vastly different swaths of the GOP electorate. The same thing happened in March's special election in Pennsylvania's 18th District — the one that Democrats were able to flip. Democrat Conor Lamb ran up enough of an advantage in the Pittsburgh suburbs to secure a narrow victory.And while Trump can boost turnout in key areas — Republicans are sure to try to deploy him strategically this fall — his support could be a double-edged sword."Trump is the greatest asset and the greatest liability at the same time," said former Virginia GOP Rep. Tom Davis. The onetime National Republican Congressional Committee chairman said that when Trump holds his huge rallies, he is able to boost support among his base, which to the president is the "red wave" he brings. But Democrats hope to use that to drive up their voter enthusiasm edge even more.Republicans hope some of their strong incumbents will be able to survive even if a blue wave develops in such suburban areas, with key districts in Florida, Virginia and New York up for grabs."You can have a strong enough life raft to make it over a blue wave if you run a really good campaign," said Blizzard.Democrats, however, say 2018 is starting to feel a lot like déjà vu for them, but in a better way: In 2010, right before Republicans flipped the House with their own red wave, many Democrats were also pointing out that they had hung on in some key special elections. But, in the races that preceded that cycle, there was still a major shift toward the GOP in most of those contests that hinted to such a Republican sweep. Today, Democratic strategists admit that they knew it wasn't going to be a good Election Night in 2010 for them based on those and many other factors.By NPR's calculations, the special elections leading up to 2010 showed an average of an 8-point shift toward Republicans. Based on that margin, predictions showed Republicans would be expected to pick up 68 congressional seats. That ended up being almost on the nose — the GOP netted 63 seats that year to flip the House.Add to that the fact that in a president's first midterm in office, his party typically loses an average of 29 seats, there are few good signs to be found for Republicans from elections this year either, much like how Democrats felt eight years ago."When you look at these special elections and you look at history, a lot of [incumbents] are going to be unable to be rescued from this wave that is coming," Yang, the Democratic pollster, predicted. Copyright 2018 NPR. To see more, visit http://www.npr.org/.