DES MOINES, Iowa -- Senator Bernie Sanders delivered his sharpest criticism to date of Democratic frontrunner Hillary Clinton tonight at the Iowa Democratic Party’s historic Jefferson-Jackson dinner.

The Vermont senator and longest-serving independent member of Congress did not say the word "Clinton" once, but he implicitly drew contrast between his voting record and the political careers of both Hillary Clinton and her husband former President Bill Clinton. He focused in on gay rights, free trade, the Keystone pipeline and the Iraq War specifically.

"In 1996, I faced another fork in the road. A very, very difficult political situation. It was called the Defense of Marriage Act. DOMA," he said, referring to the law signed by President Clinton. "And let us all remember that gay and lesbian rights were not popular then, as they are today. It was a tough vote. ... That was not a politically easy vote.

"Now today, some are trying to rewrite history by saying that they voted for one anti-gay law to stop something worse," he said. "That is not the case. There was a small minority in the house opposed to discriminating against our gay brothers and sisters and I am proud that I was one of those members."

Sanders often says that he will not make personal attacks against Hillary Clinton, but that has not kept him from drawing contrasts between himself and the former secretary of state on many issues. Still, his tone and rhetoric tonight went further. On the issue of free trade as well as gay rights, Sanders not only took jabs at Clinton, but put on her on hook for her husband's administration as well.

"After I came to Congress, elected in 1990, corporate America, Wall Street, the administration, and virtually all of the corporate media -- they said that you have to vote for this NAFTA trade agreement," he said. "I did not believe their arguments. I voted against NAFTA. I voted against CAFTA. ... History has proven that those of us who oppose those agreements were right."

He then transitioned specifically to the free trade agreement being negotiated today: the Trans-Pacific Partnership.

"That agreement is not now, nor has it ever been, the 'gold standard of trade agreements,'" he said, referencing a quote from Hillary Clinton from her time as secretary of state, when she was helping the Obama administration advocate for the trade deal. She has since come out against the trade deal.

In addition to his critique of Clinton’s voting records, Sanders made his case to the room of Democratic activists that he was ready to lead their party to victory, because his campaign alone had energy and excitement behind it. He referenced Obama's underdog campaign and said he, this time, was going to exceed expectations.

"We are going to prove the experts wrong because we are going to win this campaign. And by the way, just to remember, about eight years ago -- all of the political experts talked about how another Democratic candidate for president just could not win," he said. "He was unelectable. Remember that guy? Oh, it is President Obama. Well, Iowa, I think we are going to prove the pundits wrong again. I believe we're going to make history one more time."