Sen. Bernie Sanders went on the attack Saturday night by promising he wouldn't be "politically expedient" like his frontrunner opponent, Hillary Clinton.

In a speech to the Iowa Democratic Party's Jefferson-Jackson dinner, the Vermont socialist promised not to "abandon" any faction in America because it is simply "politically expedient." That seemed to be a shot at Clinton, who only two years ago came out in favor of same-sex marriage.

In addition, Sanders told the room full of Iowa Democrats that he will govern based on principle instead of poll numbers. The 2016 hopeful's comments are his sharpest critique of his Democratic rival since she came out in against the Trans-Pacific Partnership, an issue Sanders has consistently opposed from the start.

After explaining long held views of his, singling out his opposition to Wall Street, as well as his stances on trade deals of the past, the Keystone XL pipeline, and same-sex marriage, Sanders told the crowd, "Those are the choices I made when I came to the forks in the road. I think they tell you a lot about the choices I will make as president."

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