Why didn't Republicans become the progressive/ liberal party?

[RINO Tom]

This same topic has been covered a lot in this sub-forum, but the obvious flaw I see in your premise is the simplified assertion that (A) supporting abolition of slavery is INHERENTLY "progressive" in our modern political sense, and (B) it's even more ridiculous to act like supporting something as broad as "internal improvements" was inherently progressive - something Democrats at the time (understandably) derided as effectively corporate welfare, given American society at the time.  This amounts to the thinking that anything that led to positive ~progress~ has to be "progressive" in a left/right sense.  This is circular logic that just applies all of the good outcomes of history to the "progressives" and assigns anyone who opposed the "good" outcomes (which we view with 20/20 hindsight) as "conservative."  There were obviously left-wing GOPers who supported both abolition and internal improvements for "progressive" reasons, but there were also right-wing GOPers supporting both for "conservative" reasons.

To give a more "good faith" (if overly brief) answer, the GOP descended from the Whigs for a reason.  Once the big tent issue of opposing the expansion of slavery was out of the picture, the main two things tying the party together were nationalism and a generally pro-business attitude.  While there were obviously extremely left wing people in the GOP because it opposed slavery, it would be a mistake to think that had set the party on a natural path to be some left wing party.  The GOP was a unifying party of anti-slavery Democrats and anti-slavery Whigs ... and it seems clear that the Whig political influence was stronger.  In fact, it seems patently obvious that once slavery and Reconstruction were no longer at the forefront, the GOP very naturally and rather quickly showed its coalition's true colors.

If people want to try to argue the Whigs were to the left of the Democrats before this ... eh, I find that to be a super weak argument that is of the intellectual quality of "I just saw Hamilton and since I liked Alexander the most when it comes to race issues, he was obviously the progressive in that play."

[RINO Tom]

The Democratic party wasn't always as liberal as it is now, but that doesn't mean that the GOP had to be liberal.

The Democrats were once the establishment party and the Whigs anti establishment; many Whigs became Republicans.

Being anti establishment isn't the same as being liberal.

I do think Bryan was liberal for his time although obviously very conservative religiously.

Curious what you mean about the Whigs?  Most contemporary attack ads against them from Democrats seem to have painted them as a party of monied interests (in bed with Wall Street and the railroad companies), anti-immigration and morally judgmental.

[RINO Tom]

The Democratic party wasn't always as liberal as it is now, but that doesn't mean that the GOP had to be liberal.

The Democrats were once the establishment party and the Whigs anti establishment; many Whigs became Republicans.

Being anti establishment isn't the same as being liberal.

I do think Bryan was liberal for his time although obviously very conservative religiously.

Curious what you mean about the Whigs?  Most contemporary attack ads against them from Democrats seem to have painted them as a party of monied interests (in bed with Wall Street and the railroad companies), anti-immigration and morally judgmental.

I think that Whigs were formed as an opposition party to Jackson and that Jackson was seen as an establishment President.

Ah, gotcha, that makes sense.  However, I would argue that it in the minds of the Whigs (and quite possibly even the Democrats, with a much more positive spin, of course!), it was Jackson who was the anti-establishment figure, and his reign as President was effectively the "inmates running the asylum."  So, "anti-establishment" sentiment among the Whigs seemed to have a flavor much more comparable to "bring back the good ole days!" than "tear down the system!"

It's important to identify what the Republican Party of the era was. It was a nationalist developmentalist coalition with an aim to unify, industrialise and purify the American nation. Its planks were patriotism, Protestant moralism and the protective tariff. One could in a way compare the 19th century GOP to the interwar KMT in China: both had progressive elements, both set themselves against pre-industrial landlordism, but the parties were not "left" as a whole.

The Democratic Party represented everyone who felt threatened and left out of this drive for national modernisation: urban ethnics, labour unions, southern sectionalists, poor farmers and so on. They saw the Republican vision for America as exclusivist and hierarchical: a corrupt nexus of big business and federal government steamrolling the common man under the presumption that everyone should be a good, obedient, industrious Yankee. In this context it's easy to understand why the Democratic Party absorbed the new left and the Republican Party did not.

Great response and a much more eloquent articulation of some of the things I was at least trying to say, haha.