I disagree with you sir. The reality is, most "Trumpers" are straight ticket Republican voters. Most of them voted for Romney, McCain, and Bush in the past, and they'll vote for whoever is the next Republican candidate when Trump is no longer president. Republicans (barring a few exceptions) ALWAYS support the R candidate, where as the Dems don't. Look at 2016 for example. Both Clinton and Trump had the "Never Trump or Never Hillary" crowds in both parties, and yet Trump, when it was all said and done, did roughly equal with Romney in 2012 (taking into account how many people voted), where as Clinton did worse than Obama did in 2012. The fact of the matter is, Trump is president because Obama votes in three blue states didn't show up to vote for Hillary the way they did Obama in 2008 and 2012.
So, the Dems can't go into the midterms thinking that Trump voters won't show up and vote for the GOP, because they will. They did in 2016 (despite their complaints about the "establishment"), and they will in 2018. They know if the Dems gain control of congress, Trump's presidency is essentially finished. They don't want that to happen, which means they WILL come out and vote Republican. In order to win, the Dems NEED to come out in strong numbers and vote, as they outnumber the GOP base by a significant amount. They can't stay home and not vote, because doing so always results in a GOP victory.
Both NYT's and CNN exit polls showed Clinton received 89% of the Democratic base vote, 8% to Trump. Trump received 88% of the GOP base vote, Clinton 8%. Pretty even on the base vote. But in 2012 Romney received 93% of the GOP base vote to 6% Obama. Obama got 92% of the Democratic base vote to 7% for Romney. So Trump did worst than Romney, also Hillary did worst than Obama in 2012. One reason Obama won fairly easily was the Democratic base made up 38% of the electorate in 2012 to 32% Republican, 29% independents. A six point difference where it help Obama to a five point win. Romney did win the independent vote 50-47 over Obama.
In 2016 Republicans narrowed that six point advantage for the Democrats. 37% of the voting electorate were Democrats, 33% Republicans with 31% independents. Trump won the independent vote 46-42 over Clinton with 12% of independents voting third party. The overall result in the popular vote was a drop of Obama's five point win to where Clinton had a two point win.
The thing with Hillary is she did a lot worse in almost every voting block/group than Obama. She didn't have the Obama charisma to draw out the vote for her as Obama did. Here's some to compare.
Democratic base Obama 92% Hillary 89%
Independents Obama 47 Hillary 42
Blacks Obama Obama 93 Hillary 88
Hispanics Obama 71 Hillary 65
Asian Obama 73 Hillary 65
White Obama 39 Hillary 37
The young 18-29 year old's Obama 60 Hillary 55
women Obama 55 Hillary 54
Union Households Obama 58 Hillary 51
High School or less Obama 54 Hillary 46
College grad Obama 47 Hillary 49 Hillary did do better among college grads than Obama did. This is an exception.
But so it goes, group by group Hillary did for the most part around 3-5 point worst than Obama. She wasn't liked and she had the personality of a wet mop. She always seemed aloof to the less partisan, less ideologues, the non-affiliated in other words. She was the wrong candidate. Also look at the favorable numbers of the two candidates on election day.
2016 Clinton 38% Trump 36% these two candidates set the record for the lowest favorable rating of any presidential candidates since FDR or when Gallup and Pew Research started to keep track of favorable ratings of the two major party candidates. Neither was liked or wanted by america as a whole.
2012 Obama 57% Romney 51
2008 Obama 60% McCain 56
2004 Bush 53 Kerry 51
2000 Bush 58 Gore 53
FYI the previous record for the lowest favorable rating prior to Trump and Clinton was Goldwater at 43% 1964 and G.H.W. Bush at 46% in 1992.
Turnout is always the key. But perhaps the key here is the number of Republicans in congress Trump supporters want gone, defeated.