So this is why Republicans do a little better with each midterm and have gained control of the senate as recent as last year? I get it, a dying party keeps gaining more seats. How insightful! Look, you people better learn how to talk to white conservative men between 25-55 or you'll never have our houses back!
It's pretty simple really... the GOP base is more likely to vote. So, yes, the GOP is weaker in numbers, but because the Dems have a serious issue with getting their base out in off-years, they're in trouble. It's just a reverse of most of the 20th Century, where the GOP was the party that could get its people out in Presidential years but the Democrats had such a stranglehold on Congress.
The challenge is getting the Democratic voters out the way they do in Presidentials, not pandering to conservative white men.