Oh, a bit of side explanation since it might be relevant, how each party works for choosing candidates:
Democrats: It's basically a popularity contest. At the state level, low-level politicians attempt to first make a name for themselves, enough to be picked up into one of the countless cells and subsections of the Democrat apparatus. This is why there is such an unbelievably high number of former and current activists among the Democrats. They start on the ground level out of the political structure and get picked up when they make a splash.
From there, they continue to leverage their party acclaim into higher positions, always seeking to be brought on by someone sympathetic to the cause. Eventually, they work their way up to being the 'pet' of some politician. Having shown an unlikeliness to simply exploding and not having fallen afoul of either the machinations of their party or the realization of corruption, they now are in a position to run themselves.
From there, it's merely a matter of ambition. Aim for the highest position they think they can take, sink their teeth into it, and try to win the popularity contest.
Now, amplify this across any group of Democrats. Start small, become liked by someone in charge, use that to launch upwards. Welcome to every single democrat operation, from the lowest city position to the Speaker of the House. Nearly impenetrable to anyone not already inside of it, or who doesn't have the luck of the devil.
Republicans: It's a corporation. No, seriously. You apply for a job, work under some no-name bureaucrat. If you do well, he passes it up the chain and you get promoted. Now do this all the way to the presidency. It's a lot more orderly and a lot more boring. Where the Republicans notably break from the Democrats is that they are, like a corporation, more ready to acknowledge outside expertise. If you have valuable knowledge or experience, it lets you cut ahead in line and work your way up more quickly. Have enough of it and a bit of the good old popularity contest from the Democrats, and it can even net you major positions.