A Harvard professor and Washington Post columnist who supports Hillary Clinton and wants to advise Republicans on how to choose their 2016 presidential candidate is comparing the rise of Donald Trump to that of Adolf Hitler and urging remaining Republican candidates to unite behind Marco Rubio.“Like any number of us raised in the late 20th century, I have spent my life perplexed about exactly how Hitler could have come to power in Germany. Watching Donald Trump’s rise, I now understand. Leave aside whether a direct comparison of Trump to Hitler is accurate. That is not my point. My point rather is about how a demagogic opportunist can exploit a divided country,” Danielle Allen wrote in a new commentary in the Washington Post.