I think there are going to be more and more people bolting from the Republican Party between now and next year. Those of us who already have are not going to be in the minority anymore.
Then there will be voters who might still be registered Republicans, but, disillusioned with the party and the choices between a liberal Republican and a liberal Democrat, will just decide to stay home, write in a candidate, vote third party if available, or perhaps think, what's the difference, and just vote for the Dem.
Added to that will be the fervent Trump supporters. As Trump has now made it obvious he is a Democrat and not a Republican, his fans may decide to abandon all pretext of traditional Republicanism and even their phony conservatism and just vote Democrat. If Trump is a Democrat, then they will be too. They will follow him over a cliff if he tells them to.
No, Democrat control of both houses of congress and the presidency is not all that far fetched..