Before 1972, presidential candidates for either political party were not voted on during party primary elections. They were selected by the individual parties during their conventions held months before the general election. The delegates that went to the conventions were the most active and powerful party members from each area of the country. The conventions would be held in a big smoke-filled hall (mostly men) and various men would give speeches for the person they wanted to become the presidential candidate from their party. When all the candidates had been submitted, they would have a paper ballot vote and then count the votes to see if a single candidate got a majority. If not, they would have another vote until the favorite candidate had been selected. This process selected John F. Kennedy as the presidential candidate and Lyndon Johnson as Vice President in 1960. The first time the voters got to vote for president in those years was on general election day.
President Kennedy had been assassinated while in office in 1963 and Johnson had become president at that point, so he was the Democrat presidential candidate by default in 1964. Hubert Humphrey was selected as the VP candidate. President Johnson ramped up the fighting in Vietnam involving hundreds of thousands of young men with tens of thousands of deaths.
In 1968, the Democratic Party had control of the House of Representatives, the Senate, and the White House. They had changed federal laws and government policies as they desired. The convention of 1968 was held during a year of riots, political turbulence, and mass civil unrest. The assassination of Martin Luther King Jr. in April of that year following his opposition to the Vietnam War further inflamed racial tensions in addition to the draft and popular opposition to voter suppression. King assassination riots in more than 100 cities followed. The convention also followed the assassination of Robert F. Kennedy on June 5. Kennedy’s assassination further derailed the convention, paving the way for the pro-war Humphrey. The Humphrey–Muskie ticket, competitively failed to win the confidence of the democratic voters and so failed to unite liberals or attract anti-war voters. They would be defeated in the presidential election by the “silent majority” Republican ticket of Richard Nixon and Spiro Agnew.
In 1972, the Democratic Party included candidates for the president during the primary voting conducted from January 24 through June 20, 1972. That process was finalized during the Democratic National Convention on July 13, 1972, when Senator George McGovern was ratified as their candidate. Every Presidential Election since 1968 has been conducted where presidential candidates have been voted on during the party primaries with the winner being ratified by their party convention delegates. That process allowed the voters who voted during the primaries to play a role in who would be on the ballot in the general election.
It looks like the Democrats are in the process of throwing that out the window because they now do not think President Biden can win the election. They are playing games and want to replace him on the ballot with another person that not one single voter has voted for – essentially saying we will nullify every vote cast during all of the Democrat Primaries and a few powerful people will select a person that they think can beat President Trump. These are the same people that have said President Trump will destroy “democracy”.