You are ignoring one other factor, in determining how future U.S. elections in ‘18 and in ‘20 goes: President Donald Trump’s winning, on the majority of issues. What Congress does before then should be kept separate from what President Trump does, before then. So far, President Trump is winning, and enough general election voters will pay attention to this.
I certainly hope you are right. I remember how shocked I was when, after Reagan, people completely forgot (or disbelieved / ignored) that his policies ignited the strongest economy in decades. Trump can get the same results and people will promptly forget him or tell intentional lies that he inherited the about-to-explode economy from the magic negro. The MSM plays a huge role (obviously) in these disinformation campaigns. Never underestimate the ignorance of most of the electorate. After all, they put the most radical senator of the past 50 years into the White House believing his stupid “Hope and Change” pablum which was nothing but a cover for radical socialism.