Keynes, certainly the greatest economist of the 20th century and perhaps the greatest ever, has made an incredible comeback in the last several years. In many ways he never left. While very specific public policy prescriptions had fallen out of favor for a while, the impact he made on how economics is done and how we think about the economy lived on even through the people who thought they were displacing him. But even in addition to that framework for doing economics, the more specifically Keynesian ideas have had a resurgence for one important reason - the same reason that any scientific theory gains acceptance: it makes good sense theoretically and it fits the data.
A lot of people who are not on board, though, have been pushing back. It's notable that one of the major ways they push back is with a sort of sociological, historical counter-argument, rather than an analytical, scientific counter-argument. Peter Boettke writes:
"The main mechanism [for the rise of Keynesianism] is the shift in the nature of public administration due to the progressive era, which Vincent Ostrom examines in detail in his masterpiece in the field, The Intellectual Crisis of American Public Administration (1973). This shift in public administration changes the expectations of what public policy is to deliver to citizens, and more importantly for our purposes what is expected of the policy experts. Keynes' economics fit that demand better than the more traditional mainline of economic thinking, and the Keynesian avalanche occurred and transformed economics as a discipline and economic policy ever since. To challenge this hegemony, one must get at the root cause, which is that transformation of public administration."
Boettke is - and I don't think he would dispute this - a heterodox economist. But he's not the only one that's asserted things like this. Lee Ohanian has been on record saying things similar to this (although less blatant in saying "the politicos like it") as well. And you can look at the way the whole Tea Party movement reacts too - they don't care about economic science - they see the constellation of Keynesian ideas (even if they can't identify it as "Keynesian") as a politician-buttressing ideology. It's much like the reaction against evolution that some people have - often it isn't an analytic counter-argument at all. Instead, creationists provide a sort of botched, unconvincing "these are the political ramification of evolution" counter-argument.
And yet the narrative is remarkably persistent, despite the lack of a real argument. They categorize Keynesianism as political ploy rather than scientific theory, which relieve's them of the need to engage it as a scientific theory.
This frustrates me to no end, but ultimately this will be the narrative that needs to be defeated. It's not even a narrative that makes particular sense. Since when have politicians been elected on the slogan "I don't really care about your specific spending needs because Keynesianism doesn't go that specific, I'm just going to deficit spend on everything". Keynesianism makes horrible politics, which is part of the reason why Alex Tabarrok has questioned whether for that reason alone we need to consider alternatives (I provide thoughts on Tabarrok here) I disagree with some of the pessimism of guys like Tabarrok on "Keynesian politics", but I think his grasp of the situation is much stronger than Boettke's on this point.
Anyway, like I said - this is the narrative to beat. I plan on writing something about this in my Economic Thought class this fall - answering or starting to answer this question of "why did Keynes catch on in America?". I think it has very little to do with what Boettke has mentioned and a lot more to do with the fact that (1.) it's good science, and (2.) American economic thought extending back to the colonial period was predisposed to accept Keynes.