The whole "Blue Wave" talk started right after the 2016 election, simply because it has been traditional that the party out of power gains seats in Congress in the midterms. And since the D's were extra "fired up" (aka angry) about the Trump election, their belief was that even more people would vote D.
Then Trump started keeping his promises. The economy improved. The tax cuts were passed. (which should have been done so that took effect last year, so people would know how much that impacted them when they go to polls in Nov. (R Ad- "Hey, remember that extra money you got in your refund last spring and your paychecks...Yeah 'D' Candidate and Nancy Pelosi want to take that money from you.")
And yes, the Kavanaugh hearings, the giant clown show that went along with it, and now the (ongoing) D campaign violence, (not to mention the Project Veritas videos, Hypocricy (Ellison), along with other videos (Cinema), and "Own Goals" (Warren, Heitkamp and others), is driving independents to the R's as they are being seen as the party of the adults
And that's mainly due to the alternative news sources. Fox News, FB, Twitter, other social media, means that the MSM has lost control of the narrative. No matter how much they try to "shape" the news as the had for many, many years, they are now being constantly called out for their lies, deceit, and clear bias. And when called out they try to pass them off as "errors". But if if they were honest mistakes, then at least some of them would be favorable to the Trump (and by extension the R's) but they are NEVER in Trump's favor.