In the period prior to the Democrat primaries, the candidates will be very cordial to one another. The common message will be "we hate Donald Trump." However, once the primaries start and the polls start separating the candidates, that's when they'll turn on one another as each tries to claw their way into the lead. By the time they get to the 2020 convention, it will be all out war between the various factions.
Then they’ll turn to the one who can unite & save them ! - Hellary!