The turnout in midterm elections is normally not the same as in presidential elections. That hurt Democrats in the 2010 and 2014 elections. In those elections, the Republicans were enthused to vote and turned out in much larger numbers than Democrats.
As the chart above (from Axios) shows, that has changed this year. The turnout for primaries this year (which is indicative of enthusiasm to vote in November) was the opposite of 2010 and 2014. This year Democrats had a 57% turnout for primaries, while the Republican turnout dropped to 43%.
Considering the fact that Democrats outnumber Republicans in this country, the fact that Democrats are enthused shows there really is a good chance of a "Blue wave" this year.
The only thing that could save Republicans would be if Independents broke big for them. But considering the unpopularity of Trump among Independents, that is very unlikely to happen.
