The premise is faulty. Liberals in America (certainly the elected democratic pols) are the possibly least protectionist and most economically right-wing of all of the OECD countries.
Protectionism is most popular among conservatives in America because there's a significant part of the coalition that is older and uneducated and therefore gets screwed the hardest by trade agreements. Contrast with the upper middle class educated professionals that are a significant part of the Democratic base.
News to me and exit polls everywhere!
A sizable majority of voters with graduate degrees vote Democratic these days.
That by no means exclusively indicates a high income (finance majors with bachelor's degrees are going to make a lot more than education majors with a PhD), and it ignores the fact that college graduates as a whole still voted substantially Republican in 2014. Let's not even get into the very, very clear evidence that Republican voting and a higher income are directly linked.
Affluent and educated people are AT LEAST as much of a part of the GOP's coalition as they are to the Democrats' coalition. That should be beyond debate, but I guess it's not?
Yeah, I don't dispute that Rs are more likely to hold college degrees and be a little wealthier (the fact that they are all white helps in both of these regards). But Democrats are more likely to hold postgraduate degrees, and that group of postgraduates in combination with the gigantic portion of the democratic party that is more identity-politics motivated than class-motivated has, I think, substantially if not totally neutered the class angle in the Democratic party in the past few decades.
Which is why in opinion polls Democratic voters (not really Democratic politicians) tend to favor protectionism less than the Republicans.
