Come together, right now
When he was elected president, Barack Obama entered the Oval Office with a label of being a great unifier. He would be The One to bring a divided people together. There can be little doubt that, eight years later, he has failed miserably on this front.
Nearly every time this man speaks, he says something that polarizes rather than unites. See, for instance, his recent speech at the funeral for the slain Dallas cops. 'Unity' to this president seems to mean compliance with his ideology.
Now, it can be argued that seeking high degrees of unity among a naturally diverse people all seeking to pursue unique interests is a fool's errand to begin with. Diversity naturally, and by definition, spawns disagreement and conflict. But those differences should be welcome as it is variation that fosters progress and adaptation. Order is not maintained forcibly by the strong arm of the state, but spontaneously by individuals who voluntarily cooperate with each other to better their conditions.
Nonetheless, no 'leadership coaches' that I know of would advise an executive seeking better cohesion in a group to go about it in a manner similar to this president.