it's gonna take one more generation to get rid of the old white people that vote GOP.
the thing that's gonna kill the Dems is AOC and Barnie with these plans that are way to radical and have no way of being paid for without massive tax raises. like Barnie's plan for Medicare for All, what happens when every skyscraper in every city shuts down because the insurance companies are now defunct? and you ask a Repub and they think they wont' be able to fly on planes because of AOC in 2 years.
In 2011, the ACA was almost universally reviled. By 2017, Trump's Congress couldn't couldn't shut it down. Today, Republicans in contested districts won't even talk about repealing the ACA. This just goes to show that while most people are conservative, they resist change but attitudes can change over time. I've always seen the ACA as a bridge to universal coverage. I don't really understand why insurance companies are in the health care business anyway. Medicare is a popular program too.
AOC could not have won in most districts that only lean Democrat. She beat a complacent opponent in the primary and no Republican has a chance in her district. I'm not sure she can win then primary in 2020, we'll see. But I think her Green New Deal or whatever its called, while it isn't going anywhere, it is not doing any harm just by being posted as a non-binding resolution.
It might not take a generation to see the end of GOP strength in office. By 2030, old white Republicans will be outnumbered by non-white people and millennials. Neither group are receptive to right wingers like Trump and Mitch. If your point is we'll see lots of change back and forth between now and then, I think that you'd be right.