Depending on how you want to count it, I have been a leftist for 50 if you include when I became politically aware, or 40 years from the first time I cast a ballot. I have voted for Democrats over all these years. I supported Eugene McCarthy and George McGovern in '68 and '72 I was still too young to vote. My first ballot was for Carter in '76.
After the Vietnam War ended, the country's tone started to change. With the war over, most protests died down and very conservative politicians and churches began popping up. Row v Wade was settled law in 1973 and other than the Catholic Church, there was not much out cry from other churches. The Southern Baptist Convention passed a resolution on abortion in 1971 and reaffirmed it three years later. Part of the text reads:
"Be it further RESOLVED, That we call upon Southern Baptists to work for legislation that will allow the possibility of abortion under such conditions as rape, incest, clear evidence of severe fetal deformity, and carefully ascertained evidence of the likelihood of damage to the emotional, mental, and physical health of the mother."
By 1976, the SBC tightened its opinion, and by 1980 the Convention passed the following resolution
"WHEREAS, Southern Baptists have historically affirmed the biblical teaching of the sanctity of all human life, and
"WHEREAS, All medical evidence indicates that abortion ends the life of a developing human being, and
"WHEREAS, Our national laws permit a policy commonly referred to as "abortion on demand,"
"Be it therefore RESOLVED, That the Southern Baptist Convention reaffirm the view of the Scriptures of the sacredness and dignity of all human life, born and unborn, and
"Be it further RESOLVED, That opposition be expressed toward all policies that allow "abortion on demand," and
"Be it further RESOLVED, That we abhor the use of tax money or public, tax-supported medical facilities for selfish, non-therapeutic abortion, and
"Be it finally RESOLVED, That we favor appropriate legislation and/or a constitutional amendment prohibiting abortion except to save the life of the mother."
It took less than a decade for the SBC to do that 180. That 180 dragged the conservative churches into the GOP fold.
I bring up these points as context for what it was like for this Leftist when the U.S. started its hard right turn. The GOP pulled many liberals to the right, while Leftists held their ground. As the Democratic Party started to veer right, the party started to split ideologically into Leftists, traditional liberals, and Corporate Democrats. If we are going to have unity, then these three groups will have to work together. However, funding elections requires the Corporate Democrats to give us the money and the Left wants to end things like Citizens United, support tax increases on the 10% and Corporations, and get rid of "Right to Work Laws." Getting Corporate Democrats to support Leftist concerns has never been a winning proposition. The advice frequently given to the Left is "Don't ask, just sit down, vote Democratic, and shut up." Unifying the party will require a collective approach and all sides must be heard.