I think the modern Republican Party has taken the path it has largely due to the confluence of 3 main inputs (in no particular order)...
1) Globalization, and the resulting economic & cultural disruption, has harmed the rural and semi-rural areas that the largest part of Republicans tend to live in. A lot of jobs have been lost and, in doing so, a lot of ability for those rural areas to retain people have been lost. Another big part of the issue in these communities is that those left behind simply don't have the same standard of living they had before and they greatly fear losing the standard of living they currently have. A loft of folks are upset that younger folks don't have a great economic future in their small towns and therefore choose to leave to go where greater opportunities are. Additionally, globalization and its effects have brought folks into these rural communities who were not there even 20 years ago, often people of color, which have changed the way these communities see themselves. And so for many in these communities, they are very, very upset about both the economic and cultural changes that globalization has brought to their communities and they have chosen to both lash out at those they believe to be responsible for those changes and to take any steps they can to ensure that the remaining "economic pie" in their area goes to those like them and not folks they see as "others".
2) Demographic change has also been a significant input into the Republican push away from conservatism and toward authoritarian fascism. What Republicans see is a number of demographic changes to our country, all of which either scare them or which don't benefit them politically (or both).
- Urban areas continue to grow in both numbers and power, while rural areas experience "brain drain" and loss of power.
- The country is increasingly becoming one of racial/ethnic diversity. (Although Pubs have made a good run at Hispanic/Latinx folks over the last few years.)
- Women are increasingly taking hold of leadership positions, great and small, and are increasingly free of traditional gender restraints.
- Increasingly, minority groups who used to be content to hide themselves/remain on the margins of society are pushing for equality and a greater place of acknowledgment in and by society.
What Republicans have taken from this that their opportunities to both remain in power and/or use the power they obtain to keep a "traditional" society intact has and is greatly weakening. A pivotal event in this process for Republicans was Obama's election in 2008. Beyond electing on person of color to the presidency, the overwhelming nature of Democratic gains in Congress was a kind of shock to Republicans that let them know that without a major change that the long-term prognosis for their party and their desired America was not good. It lit a fire under a lot of Republicans, both leadership and, more importantly, proto-MAGA party members.
3) Republicans have been radicalized for the last 40-ish years and we're seeing the long-term fruits of those efforts. Republicans have been taught by right-wing media and, increasingly, by actual Republican politicians that Democrats aren't just folks with whom they have disagreements, they are the enemy. That policy differences aren't merely differences in opinions, goals, or perspectives, but that they will lead to the end of our country or society. That there is no way that Republicans can co-exist with non-Republicans because the differences are too great, that the only potential outcomes are either Republicans win and the country is "saved" or that Republicans lose and the country is "lost". And once a significantly large group of folks view the world in this black-or-white, right-vs-wrong manner, then there is no limit to what is not only acceptable but beneficial to ensure that the terrible things promised if "the others" should win does not happen. This is radical extremism no different than that which undergirds terrorism or revolutions. (Of course, the ironic thing is that in becoming such a radical body, Republicans have made themselves into the very type of extremist group that justifies the rhetoric being applied to them that they used against their opponents without actual reason.)
The combination of these 3 factors led Republicans into leaving conservatism behind and morphing into a body largely taken with authoritarian fascism. Their desire to preserve traditional hierarchies, norms, and social orders - when faced with forces that threatened to provide support for different priorities and outcomes - led them to reject full democracy, small government ideas, and even the rule of law for the raw power to attempt to preserve the social order and their place in it.