It would have been undignified, but it might have worked.....

[Binders Keepers]

if the other Republican candidates had formed a gentleman's agreement at some point to take Trump out of the game. And this is how they could have done it: Trump delighted in skewering his opponents with a withering nickname: "Low-Energy Jeb," "Lyin' Ted," "Little Marco." If the rest of the field had responded by unanimously referring to the Donald as "Stupid Donald," his head would have resembled a tea kettle at boil. In this way, they could have ridiculed his ideas as patently absurd: "Stupid Donald thinks it's smart to build a wall...." You have to give bullies a taste of their own medicine. Trump is such a prickly character that I think this would have been devastatingly effective, especially if parroted by all his opponents.