Story highlights

Sanders said Clinton's email scandal is "clearly not helping" her campaign

The Vermont senator also weighed in on GOP front-runner Donald Trump, saying he's made racist comments

Washington CNN  — 

Bernie Sanders said new polls that show him drawing even with front-runner Hillary Clinton in key primary states are stunning.

“You want me to tell you the truth?” he asked to CNN’s Wolf Blitzer in an interview Thursday when asked about his strong showing.

“Yes, I’m stunned,” Sanders said. “Look, we have a message that I believed from day one was going to resonate with the American people. … Did I think (the issues) would resonate as quickly as they have? The answer is no.”

RELATED: Sanders evens with Clinton

Sanders credited his focus on middle-class economics and anti-establishment message as keys to his success.

A Quinnipiac University poll released Thursday showed Sanders continues to build momentum against Clinton, puling even with her in Iowa, 41% to 40%. That’s up from a 21-point deficit with Clinton two months ago. Other recent polling that has shown Sanders ahead in another key early primary state, New Hampshire, although Clinton still maintains double-digit leads in national polling.

Sanders said his campaign has received contributions from more than 400,000 people with an average donation of $31.20, while eschewing raising money for super PACs.

As for Clinton’s inability to move past the scandal over her use of a private email server as secretary of state, Sanders wouldn’t quite say it was hurting her standing.

“I think it’s clearly not helping her,” he said.

The Vermont senator, who serves as an independent in Congress and has identified as a democratic socialist, was pressed on whether he was a true Democrat.

He said it’s “no secret” he’s an independent in Congress, but he has always caucused with Democrats.

“I am going to be doing everything that I can to see that the Democratic Party is successful in November,” he said.

“I am a proud progressive,” he added in response to Clinton telling an Ohio crowd on Thursday that she’s a moderate.

RELATED: Clinton to Trump: Bring it on

He also didn’t get into whether Vice President Joe Biden should jump into the race, an option the vice president is weighing with this family.

“I neither want him to jump or not want him to jump in,” Sanders said. “That’s a personal decision that he has to make.”

Sanders also weighed in on the Republican side of the race, including GOP front-runner Donald Trump.

“I think he’s obviously a very flamboyant guy,” Sanders said. “I think he’s clearly doing a lot better in the Republican process that anyone thought he would. I am sad to say that in the year 2015, people like Trump are using racism as a way to attract votes.”

The senator specifically hit Trump for comments he made about some illegal immigrants being rapists and criminals.

“His remarks were totally objectionable and they were racist,” Sanders said.