Why do good people who are Republicans act so bad regarding their government?

[Southern Senator North Carolina Yankee]

You cannot begin to understand the current political divide by looking to any point in living memory of anyone alive today.

We have an immense cultural divide that defines the two parties. We have a partisan press that caters to each side, with the positive feedback loop and confirmation bias that tailored search engines and recommended lists on various social media sites tend to create. This means that both worlds live in their own universe with their own priorities and their own truth.

Furthermore, they view the success of the other side as a fundamental destruction, an existential threat to the continuance of their culture, their political and social norms and their political wish list. To put it bluntly, it is a figurative fight to the death with the highest stakes attached to victory or defeat, possible.

The closest parallel that can be informative is the post Civil War period. This is often wrongly taught today emphasizing too much that there was a "lack of disagreement" between the two parties. This is fundamentally false, appropriating modern understandings of policy (especially economic) onto a past period. The Republicans, the party of Yankee whites and the Democrats, the part of White Southerners, Irish and other immigrants. The Democrats viewed the success of their opponents as an existential threat to either Southern culture or Irish political and religious rights, or both. Republicans viewed the success of the Democrats as an economic threat risking complete devastation to their wealth and power achieved in the Industrial Revolution and also a demographic threat in the form of displacement by immigrant groups (some things never change).

They each had their own newspapers, they each had their own "truth" and unity was maintained as much in opposition to the other side as in favor of any particular agenda, ideology or philosophical underpinnings.

Not surprisingly corruption during this period was rampant and it was tolerated and waved off, because while a Republican might be a crook, at least he will keep the tariffs high and put the Irish in their place, likewise a Democrat might be a crook but at least he will protect the immigrants and put the... (you can fill in the rest in your minds).

 It also worth mentioning that corruption itself takes on a partisan meaning. You see this every time one party raises hell about some behavior only to do it themselves. Also to the fervent diehards, the opposition party's agenda is itself the product of corruption. You saw this with conservatives viewing the green agenda as a slush fund for rich liberals in California and likewise Democrats seeing Republican policies as "corrupting the system" to benefit the rich. Once you play this out, the word corruption loses its objective meaning and becomes solely anything that the other side is doing, which by extension means that simply by opposing them and defeating them you have in your eyes, "drained the swamp". In Trump's eyes and many of his supporter's eyes, he "drained the swamp" when he defeated Hillary Clinton. His grifting since is either ignored, deemed irrelevant or even more blatantly embraced on the grounds of, well they had their turn at it, now it is ours (NC GOP on redistricting right there).

That is literally where we are at. "He might be a crook, but at least he is 'our' crook". The good news is, sooner or later this paradigm breaks.