Is that what your professor told you?
Notice how you didn't answer the question. . .at all.
Here's what happened: In the early part of the 20th century socialism was the new and exciting thing. It was sweeping Europe but simply not taking hold in America. Editors like Walter Lippmann and periodicals like The Atlantic bemoaned the situation. They wrote that the world was being transformed and America was sitting it out. Liberalism at that time meant Constitutionalism and conservative meant old, staid, and ossified (wasn't even really much of a political term then). Democrats and Republicans were both Constitutionalists and expressed their opinions within that framework. Socialists were outside of that.
Something had to be done. So Lippmann et al. along with their political supporters like Woodrow Wilson agreed to rebrand socialists as "Progressive." Lippmann himself wrote that nobody in their right mind wants to stand in the way of "progress" so naming themselves "Progressive" instead of "socialist" is the way to convert the people with minimal effort. They were largely successful. Teddy Roosevelt was the first Prog candidate under the Bull Moose Party.
But then the abject terrors of Progressivism blossomed in all their putrid horror. Before WWII Hitler was hailed on the west side of the Atlantic as a Progressive force changing the world for the better. Lennin and Stalin both were Prog heroes in America. The Holocaust and the advent of the Cold War changed everything. Progs could no longer associate themselves with Nazis and Soviets even though they promoted them for decades. They had to come up with a new plan. Their plan to rebrand worked before so they figured it would work again. Rebrand!
So they (Lippman et al.) commandeered the term "liberal" to mean "socialist/Progressive" and labeled the Constitutionalists as "conservative" and wrote about it in The Atlantic. Word spread through the NYT and other newspapers. Soon the old ancient idea of dictatorships became the "new" thing and the new liberal idea of self-governance was "conservative."
Then of course, 2008 came along and Americans had finally seen the light again. "Liberal" meant "socialist" because you can only lie and hide the truth for so long. Time to rebrand again. And so Hillary Clinton rebranded liberals as "Progressives" because enough time had elapsed between the Prog horrors of despotism, eugenics, and genocide that she figured people will have forgotten the true meaning of the word "Progressive."
You're welcome. What's that? Want proof? Linky linky?
No soundbyte or quicky linky will suffice. It's a rather large concept requiring multiple links, quotes, and references. You can find them all here:
All original sourced material so you can forego the dismissal based on politics. These are the original words in the original context without the professorial filters and references to other references to other mistaken references. They cut right through all that academic crap and address the original text in the original context.
All for free. Again, you're welcome.