yep, both parties were moving left before
It begins in 1986 when moderate democrat Joe Lieberman formed the DLC under the premise that if the democrat party kept nominating leftwing populist candidates like Walter Mondale to run against moderate republicans like Reagan, the dems could never win the presidency.
Bill Clinton became head of DLC after Lieberman which he rode to the Presidency and would be known as the 3rd way compromising New Democrat willing to cut a deal with the moderate Main Street republicans. Clinton infuriated the left wing because of his involvement in NAFTA and Welfare Reform so the left wing began calling the DLC the republican wing of the democrat party.
Then DLCer Al Gore won the dem nomination and had DLCer Lieberman as veep.
Karl Rove invented the term Compassionate Conservative that Bush would use to try to push Gore off of the center.
But the left prevailed. Leftwinger Ralph Nader syphoned 80, 000 votes away from Gore in Florida, allowing Bush to carry the state with 700 votes and become Prez.
Then in 2008, Obama campaigned to the left of Hillary and the leftwing loved him, but after becoming prez, Obama became more centrist than Hillary, so now the leftwing detests Obama not just because he is moderate but also because he lied to them.
Now, faced with the prospect of Hillary winning the dem nomination, the leftwing is agitating for leftwing Mondale democrat Elizabeth Warren to challenge Hillary for the nomination.