Former Republican presidential candidate Mitt Romney has been openly critical of Donald Trump, and of the Republican Party s continued support of the bombastic billionaire for president. Now, one of his former campaign operatives has written a stunning op-ed in which he roundly trashed Donald Trump and gave a rather glowing endorsement of Democratic nominee Hillary Clinton. That man is David Nierenberg, Romney s former finance chair. The piece appeared on CNBC s website. Nierenberg says of Hillary Clinton: Hillary Clinton knows her stuff. She is emotionally mature and centered. She respects and enjoys working with people from all backgrounds.She has the diplomatic skills needed to break the gridlock in Washington and lead our country well. America needs a steady hand on the tiller. Despite being a Republican with ties to Mitt Romney dating back to 2006, Nierenberg had this to say about his party s current standard-bearer: Trump is the most dangerous major party presidential candidate in my lifetime, maybe in American history. His character, temperament and behavior are definitely not presidential.I don t think he s fit to be our president. He speaks positively about foreign dictators and acts like one himself.This year, however, watching and listening to Donald Trump s erratic daily bullying, ranting, bragging, scapegoating and name-calling, my conscience and my three adult children will not let me vote for him. Nierenberg also joined the call for Trump to release his tax returns. He said: For decades, candidates, including successful business people, have released their tax returns; why does Trump think he shouldn t follow the rules of the game? Defeating him has to be our national priority. He is exactly right. This is a time to put party before country. This is no longer about left versus right, Republicans versus Democrats. This is about having one candidate in what is, for all intents and purposes, a two-party political system who is qualified versus one who is a dangerously unfit demagogue. The choice is ours, America. Put party before country and vote blue in November.Featured image via Instagram