I have had several posts (this is the latest) trying to explain why American conservatism became ideological, but wasn't satisfied with any of them. I identified several factors that might facilitate that developmetn, like a sense of being embattled as education and the media came to be dominated by liberals, but no primary impetus. Now I think I've found one, suggested by Irving Kristol in his Neoconservatism: The Autobiography of An Idea (with an assist from Samuel Huntington, American Politics: The Promise of Disharmony). It is "the fact, noted by all historians and observers, that the United States is a 'creedal' nation" (Kristol, p. 376). That creed has canonical texts (the Constitution and Declaration of Independence), which means that there's a possibility of "fundamentalist" movements that say we need to go back to those texts in order to find the answers to our problems. Of course, liberals can do that too, especially with the Bill of Rights, but it's hard to deny that the founders saw only a small role for government, especially the federal government. So after the appearance of social welfare programs and the rise of the "administrative state," appeals to the Constitution had a better fit with conservatism. This was what led American conservatism to become ideological--it wasn't just an appeal to "tradition," which can mean many different things, but to to specific ideas expressed in specific documents.
Although I think Kristol had the right answer, he had the wrong question. He thought that the exceptional feature of American conservatism was that it was populist. There is a strong populist tradition in America, but populist conservatism is different from ideological conservatism. Kristol held that the people had an instinct to do the right thing (as he saw it): "today  populist opinion--as every poll shows--is more concerned about cutting the federal deficit than about lowering taxes, which as come as a great surprise to many [traditional] conservatives, who learned in their 'political science' classes that 'the people' always want to be pandered to" (p. 384). In reality, popular opinion reliably favors low taxes and "don't tread on me" rhetoric, but also programs like Social Security and "reasonable" regulation of business.
The division between the populist and ideological stands of conservatism explains the collapse of the "repeal and replace" effort. The populist position would be to keep the parts that imposed burdens on large employers and insurance companies, but drop those that imposed burdens on ordinary people--taxes and the individual mandate. The proposed act was a compromise between the populist position and the generic conservative inclination to scale things back and cut costs, so it was unacceptable to people who were serious about getting the government out of health care. But a program that really got the government out of health care would be totally unacceptable to the public, so that meant that there was nothing that could get the votes to pass.
Of course, there is always a division between people who want to go farther and faster and people who are more cautious. But the divisions are especially contentious in this case because the ideologues see the mainstream conservatives not just as timid, but as traitors to the cause. On the other side, the behavior and public statements of the mainstream conservatives about the ideologues have been restrained, even deferential. There are occasional expressions of irritation, but nothing like the constant attacks on "RINOs" that come from the right. I think the reason is that the mainstream conservatives give the ideologues credit for standing on principle, maybe even see them as "the conscience of the party." As a result, the ideologues have a disproportionate influence.