WASHINGTON -- With 30 weeks left till the Iowa caucuses, where the first votes will be cast on the way to the presidential nominations, the Democratic race for president appears to be tightening as Vermont Senator Bernie Sanders gains momentum.

It was another full house for Sanders Monday night in Portland, Maine, where he made his populist pitch to 7,500 supporters.

"We are going to send a message to the billionaire class, and that message is, you can't have it all," Sanders told the crowd.

With a promise to fight income inequality and take on Wall Street, the Vermont Senator is closing in on Democratic frontrunner Hillary Clinton.

One recent Quinnipiac University poll showed Sanders doubling his support since May in Iowa. Sanders says he's surprised by the numbers.

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"Our campaign is moving faster," he said. "I mean I thought we would catch on, but I think we're catching on faster than I would have thought."

It's come without the money or organization of the Clinton machine. In the last fundraising quarter, Sanders raised $15 million from 250,000 people -- a strong grassroots showing, but pennies compared to Clinton's $45 million. And that's not counting the more than $23 million raised by Super PACs backing her.

When asked if he can go up against the Clinton juggernaut, Sanders answered: "Yes, I really do. When the American people are saying enough is enough, we have to stand together to take on big money interests, when that starts galvanizing, there's nothing that's going to stop us."

Tuesday in Iowa City, Clinton welcomed the challenge.

"This is going to be competitive, it should be competitive, it's only the presidency of the United States we're talking about," said Clinton.

Clinton's press conference Tuesday is part of a new strategy to make her more available to the national media. Clinton advisers say they always expected a primary challenger but they don't see Bernie Sanders as a real threat.