That's the opinion of political analyst Charlie Cook (pictured). Here's some of what he had to say about this in a recent article for the National Journal:
Republican hopes these days rest on two things. First, their deficit on the generic congressional ballot seems to have declined from 13 points in late December to about 5 points now, according to the FiveThirtyEightaverage of polls. It’s plausible that passage of the tax-cut bill in December put a bit of starch in Republican voters’ shorts. There is a general feeling that because of where the lines lay, Democrats need to win the national popular vote for the House by somewhere in the neighborhood of 7 to 9 points. The GOP’s second hope is that the economy will remain strong through the election and that at some point, President Trump and congressional Republicans will begin to get some credit for it. But while these high hopes were emanating from last week’s Republican congressional retreat at The Greenbrier, data from individual races on both the district and statewide level reveal that the plight of Republicans actually appears to be even more difficult than it seemed last fall. This is particularly true with individual-race polling, but other indices such as candidate recruitment and campaign fundraising are sending “Danger, Will Robinson!” messages. This is particularly true in the House, where there are quite a few GOP incumbents in competitive and potentially competitive races who are not raising the kind of money they will need if there is much of a Democratic wave at all. The fact is that Democrats were on the unfriendly side of two wave elections in the last decade, in 2010 and 2014, while for Republicans, it has been a dozen years since the GOP got hit with one. In 2006, when President George W. Bush’s last Gallup job-approval rating before the midterm election was 38 percent (sound familiar?), Republicans lost both their House and Senate majorities. There is a lot of cherry-picking poll data, searching out the most optimistic numbers around, that seems to be giving some Republicans a degree of complacency that is at odds with averages and hard data. In an analysis released Sunday of more detailed data from the Jan. 15-18 ABC News/Washington Post poll, much of the national 14-point Democratic lead among likely voters in the generic-ballot question was among voters in districts already represented by Democrats, where they had a 38-point lead—64 to 26 percent. This no doubt was a finding that encouraged Republicans, but the analysis also revealed that in districts already represented by Republicans, the GOP advantage on the generic was just 6 points, 51 to 45 percent. In other words, Republicans have a lot of districts where their leads are very, very narrow while Democrats have very big leads in their districts. It wouldn’t take that much of a wave for a large number of seats to drop against the GOP. The serious Republican strategists that I have talked with in recent days are extremely worried about this election, and what they are thinking and seeing doesn’t match up with much of the happy talk coming out of The Greenbrier.