Note: I started writing back in late September but fell short of ideas.
I've written about this before, but this requires more attention than what it's gotten. Most of everyone tend to call them "liberals". The left first started playing with it by late 1910s when the American people became hostile to progressive with Woodrow Wilson entering us into WWI when he initially promised not to get involved.
Also taxes were raised and government grew dramatically. Notable products of the Progressive Era are the dreaded 16th (income tax) and 17th (direct election of Senators) amendments. Everything that's happened since can be traced back to these amendments as they've allowed for near unlimited growth, size and scope of the federal government.
Now when everybody realized what progressivism really was they immediately back with electing Warren G. Harding to the White House (and later Silent Cal who succeeded him upon his death). So the left realized they had to adopt a new term. They decided to go with liberalism which ironically really means exactly opposite of what they pined it as which is free markets, small government and individual liberty (still does actually across the pond and other parts of the world).
Eventually they pulled success with this word by electing FDR in 1932 who was the first politician to identify as a liberal in the new context and pushed through the New Deal and dramatic expansion of the federal government. Key policies such as Social Security were passed along with the New Deal. FDR's 1st term was relatively successful in getting what he pushed for passed. Even the Republican Party initially supported the New Deal. Though with his 2nd term like Obama is now he got arrogant with power with pushing to stock the Supreme Court with leftist appointees.
Unlike now where Sleazy Harry does whatever the hell O wants, despite there being Democrat super-majorities his own party stood in principled opposition. And in this there was a quasi coalition formed between Republicans and conservative southern Democrats which continued on into the mid-1960s. And this was one of them. 1938 was the bloodiest midterm for an incumbent president in the 20th Century. The Democrats lost I believe it was 75 seats in the House (correct me if I'm wrong) and lost 7 seats in the Senate.
After that, FDR went on to a 3rd term and had his high points with WWII though that's another diary for another time. Fast forward a bit we have LBJ's presidency which would be the third in a line of four that passed massive new welfare entitlements and expanded the federal government's scope and power. He of course got through the Great Society and affirmative action. Both measures of which proven to have failed miserably in course of 50 years. Nixon was elected as someone who'll change direction, but basically continued on LBJ's policies.
Then Jimmy Carter was elected and his presidency scared everybody away from modern liberalism in favor of Reagan conservatism in two landslide elections ('80, '84). The left realized that liberalism wasn't appealing any longer so came along Bill Clinton who tracked the Democrat Party back to the center giving them their first presidential victory in 16 years. And it remained pretty much there until sometime in Bush II's presidency and Obama's '08 campaign. What's interesting about '08 is that Hillary rejected liberalism and adopted progressivism instead.
The left adopting progressivism once again gives us the right a chance to reclaim liberalism in its original sense but that's another diary I'll write. Progressivism had a nice ring for awhile like it did before in the early 20th Century, but with Obamacare people are now waking up and abandoning in droves with Obama's numbers in the bunker still. The left has been successful for a century's time in switching out terms so as to disassociate themselves from the policies they installed under that banner. However that is increasingly becoming more obvious with Obamacare's self-destruction going on. I personally prefer to use the term progressive as it's what the left truly is, but leftists are leftists whether liberals, progressives, socialists, fascists or communists. Thanks for listening.