As parties began to develop ...

As parties began to develop around the turn of the 19th century, you had party nominees for President nominated in caucuses made up of party members in Congress.
 Michael Beschloss

Quotes from the same author

So if 1960 had occurred under the old convention system, Kennedy would have had a very hard time getting the Democratic nomination because he would have been rejected by all those people who had worked with him in Washington.
 Michael Beschloss
So the result was that as one approached a political convention for most of the 19th century and for most of the 20th century until the 1960's, part of the drama was the fact that you didn't know ultimately who was going to be the nominee at the end of that convention week.
 Michael Beschloss
Under the system that we now have to nominate presidential candidates, for instance, I would prefer that we have a system that is closer to, say, the one we had in the 1960s.
 Michael Beschloss
Then you get to the last half of the 20th century, Americans are getting very skeptical about their leaders and their institutions, and another place that is affected is parties and conventions.
 Michael Beschloss
Lincoln was able to say, you know, "It will make me very unhappy if I lose the presidency, but I'm committed to larger things." If you look at candidates and say this is someone who can be happy to go back to their family or they have larger convictions. Franklin Roosevelt jeopardized his presidency by telling Americans in 1940, "We might have to fight Hitler." He loved being president, but he loved defending freedom more.
 Michael Beschloss