It’s not half, more like about 1/3, but it’s also a little more complicated than that. Basically it’s all the fault of the first past the post voting system. Because of that, the only winning strategy is a two party system, any party beyond the main two only functions as a spoiler for one of the two. As such, a lot of different policies that aren’t really connected in any way end up mashed sort of arbitrarily into one of those two parties. Republicans due to events in the Nixon presidency ended up latching onto evangelical Christians, policies that favor the rich at the expense of the poor and middle class (usually spun as fiscally responsible), and racists (lots of overlap between evangelical Christians and racists, so that’s almost redundant). Over the years the economic policies have gotten a fresh coat of paint by way of the debunked trickle down economics theory which was used as a rallying cry to oppose any regulations such as environmental and pollution controls, or policies that favored the public at the expense of corporations because the “free market” would solve all problems. Democrats then embraced essentially the opposite of all of those positions, so wound up with socially progressive policies almost by default as reactions to the policies being pushed by the racists. This is for instance how Democrats ended up being pro-choice, as the Republicans had taken an anti-abortion stance at the urging of the extreme elements of their Christian demographic.
Ironically we’ve come full circle now with Republicans ending up with many policies by default in reaction to policies being pushed by Democrats. The Republicans of today are mostly defined not by any particular policy or goal other than their historical ones and a broad opposition to all policies pushed by Democrats. They general don’t have a stance on a policy until they hear what the Democrats position will be at which point they take up whatever the opposite of that is. This is part of how Republicans ended up as the party of the gun nut. The Democrats in the late 80s and early 90s attempted to pass some gun regulations which angered the largest gun manufacturer lobbying group, the NRA, who then spent the decades since then painting the Democrats as wanting to repeal the second amendment and disarm the American public. This in turn has led the Republicans to fully embrace removing and opposing any regulations on guns.
As the generations that grew up in a segregation era US are dying off though the Republicans are finding themselves with increasingly diminished support for their racist policies. Compounding that is that decades of free market policies and consistent push back and removal of regulations has demonstrated that the “free market will sort it out” claims are complete bullshit and just leads to things getting worse, not better, at least to anyone who has been remotely paying attention. As a result we’ve recently seen the Republicans pivot to embrace anti-diversity policies such as opposition to pro-LGBTQ policies (once again driven at least initially by their religious extremists) as well as policies designed to white-wash past racism and push a revisionist American history that paints the American civil war as primarily being motivated by disagreements about the structure of the US government rather than about opposition to ending slavery.
Forty years ago the Republicans were an even mix of racists and conservative economic policies. These days they’re mostly just the racists and a small minority of true believers in trickle down economics. Since they no longer have the numbers to win elections legitimately they’ve increasingly embraced various anti-democratic policies that allow them to retain control. Until recently, relatively “normal” tricks like gerrymandering and voter suppression in conjunction with a generally lukewarm support for Democrats (who have had their own issues of late, mostly around running profoundly milquetoast candidates) have allowed the minority of Republicans to maintain control. Now that even that no longer appears to be enough to keep them in power they’re increasingly turning to outright illegal activities like voter fraud and as we saw on the 6th, insurrection. While not every person who votes Republican takes part in or even supports such illegal activities, it’s quickly approaching the point at which they will need to confront the fact that those tactics have become a core part of their parties policies, so continued support for the party is tacit approval of such tactics. Many of them no doubt will continue to support the Republican party under a ends justifies the means stance, but hopefully the misguided ones who legitimately believe in trickle down economics can be convinced that such tactics are a bridge too far.