Lindsey admitted in December of 2016 that Russians had hacked his campaign email. Shortly after that is when he did his complete 180 to being one of Trump's most vocal defenders. I'd say there is a 100% chance that Russians have compromising information on him with a 0% margin of error.
That might explain Lindsay, but fails to explain how so much of the GOP fell lock step behind Trump and will ride his coattails to their own political graves if need be.
I think a simpler explanation exists vs. “vast Russian conspiracy”. Republicans will bow before Trump because they’re convinced they need his base to win elections. They’re banking on 2018 being a standard midterm shuffle and think they’ll win 2020 as long as the economy keeps on humming.
Why do they need a base of deplorables? They can keep cozying up to billionaires, big oil, banks, corporate lobbyists, churches etc. to raise money, but at the end of the day they still need votes.
The GOP has fully embraced identity politics because without it, they are unelectable. The demographics have shifted and their old base of white baby boomers are becoming less relevant—it’s their kids and grandkids that the GOP needs to cling to though. Their reliable single-issue voters (anti-abortion, pro 2A etc.) just aren’t enough to win elections anymore. Deplorables + evangelicals is the way to go. GOP members may not really care about Trump’s agenda, but you can be sure they care about winning elections.