Transcript for Bernie Sanders: 'We're Going to Make History One More Time'

The presidential campaign with took a turn overnight, with Donald Trump raising questions about Ben Carson. Carson demanding an apologize and Donald Trump is standing by live to respond. And Bernie sanders sparks the sharpest contrast with Hillary Clinton. Echoing the Iowa speech that launched Barack Obama's launched Barack Obama's campaign eight years ago. Good morning, David. Good morning, George. Bernie sanders never mentioned her by name. As he ticked down the issues, the environment, the Iraq war, same-sex marriage, he made the case that his views haven't changed with the polls, sharp elbows there just as Clinton was beginning to breathe easy. Just 99 days until the Iowa caucuses and Hillary Clinton is enjoying a comeback. Fans and supporters gathered early, serenaded by pop star Katy Perry, dressed like a patriotic superhero. Hillary Clinton is the woman of the hour, but does she have the nomination locked down? Got a warm reception last night. I'm not running for my husband's third term and I'm not running for Barack Obama's third term. I'm running for my first term! Reporter: But don't count your opponents out just yet. Everybody saying it's all over D you not get the message? Vermont senator Bernie sanders laughs off that suggestion. I think we are going to prove the pundits wrong again. I believe we're going to make history one more time. Reporter: He's now taking some of his sharpest shots yet at Clinton. Calling her out for flip-flopping on the president's new trade deal, for instance. Clinton had called it the gold standard, now, she's against it. That agreement is not now nor has it ever been the gold standard of trade agreements. I did not support it yesterday. I do not support it today. And I will not support it tomorrow. Reporter: Still, it caps off what may be Clinton's best week since she announced her candidacy. Not only did three potential rivals, including vice president Biden, clear out of her path, but she managed to hold her own at the benghazi hearing. I'm sorry that it doesn't fit your narrative, congressman, I can only tell you what the facts were. Reporter: But Clinton's worst enemy could still be herself, there's still that FBI investigation of her e-mail server and the fact that she's a partisan lightning rod. Hillary Clinton. Hillary Clinton. Hillary Clinton. Reporter: Her own remark calling republicans enemies prompted Biden to chastised her. I don't consider republicans enemies, they're friends. Reporter: Clinton still needs to prove that she can unite people. Her nomination is clearly hers to lose. The fact on the ground here is Katy Perry aside, Bernie sanders is generating more excitement as measured by larger crowds and smaller donations. He's a force to be reckoned with. Things also heating up on the republican side.

This transcript has been automatically generated and may not be 100% accurate.