I am often asked by people I represented in South Florida, "What happened? How was the Golden Age of Askew, Graham, and Pettigrew lost?" The answer is simple--math. And Reapportionment. And the Electoral College. Here is my description of the chronology:
1964 President Lyndon Johnson pushed through the Civil Rights and Voting Acts, over the objection of the majority Southern Democrats. LBJ, intent on having the press remember his courage (overlooking Viet Nam) predicted the end of the Democratic Party.
1968 Democratic Nominee Senator George McGovern split the Democratic Party into Caucuses, which isolated the Southern Conservatives from the rest of the Party. Conservatives left the Democratic Party in droves. McGovern lost 49 of 50 states.
1972 and 82 Reapportionments. The Republicans pushed a "Trojan Horse" of single member districts as a minority issue. The Democrats bought it hook line and sinker. The Republicans carved out a hand full of seats for African Americans, and there was peace.
1992 and 2008 Only the extraordinary candidacies (and third party candidates Ross Perot and Ron Paul) of Bill Clinton and Barack Obama got the White House back for the Democrats. The Congress, State Governors, and State Legislatures mostly continued to be taken back by the Republicans. The country has remained evenly split between red and blue for abut 40 years, but with the control, the Republicans gerrymandered the states and congressional seats for lock down control.
Today. The Democrats cannot understand how they have the most votes for a candidate, but they overwhelming lose. The answer this year was their candidate, but the heart of the issue is math, Reapportionment and the Electoral College.
The only answer for the Democrats is to roll up their sleeves and start winning back state by state. But that is very unlikely with the noise and immediacy of the press and social media.