I fail to see this. The GOP has it s biggest majorities ever. And it's not like the Democratic Party of 1932-64 which depended a lot on its conservative wing for its numerical majorities.
Roy Moore isn't that far away from mainstream conservative Republicans in anything but style. The GOP only has a few Republicans in the Northeast that are "moderates", and even they are closer to the National GOP than, say, John Stennis was to the National Democratic Party of his day.
The Republicans have always been more pragmatic than the Democrats in terms of viewing what there was to lose.
Biggest majorities by what standard? They have a minority President and modest majorities in both houses of Congress, far below the biggest they've ever had.