Every candidate in the 2016 presidential race talks about responding to income inequality and stagnant middle class wages. No one else talks about it like Bernie Sanders. The self-described socialist senator from Vermont wants to reverse the "massive transfer of wealth from the middle class to the top one-tenth of 1 percent." The 90 percent top income tax rates America had during the 1950s might not be too high, he said.

He wants big Wall Street banks broken up. He's willing to accept slower economic growth in return for what he'd consider a more equitable distribution of income.

Sen. Bernie Sanders, I-Vt. Tom Williams | CQ Roll Call | Getty Images

"The issue we're dealing with is actually the struggle to rebuild American democracy," Sanders said in an interview at a Capitol Hill bistro. "Economically, over the last 40 years, we've seen a middle class in this country disappearing. "Ninety-nine percent of all new income generated today goes to the top 1 percent. The top one-tenth of 1 percent owns as much wealth as the bottom 90 percent. Does anybody think this is the kind of economy we should have. Do we think it's moral?"

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Sanders acknowledges the long odds against his attempt to upset former Secretary of State Hillary Rodham Clinton and capture the 2016 Democratic presidential nomination. But he's interested in advancing his ideas even if he doesn't win. And at a moment when rank-and-file Democratic voters are gravitating toward more robust economic populism, Clinton's campaign is watching his efforts closely.

The one-time mayor of Burlington decided months ago to pursue a campaign only if he had confidence that it wouldn't be a counter-productive flop. "If I do badly, and I don't run a good campaign, and we don't get our message out, and we don't bring people together, it reflects not just on me, but on the ideas that I'm talking about," Sanders said.

But he added: "A couple months ago, I was in California, a beautiful sunny day. We had 500 people coming out at a union hall. I went to Austin, Texas—we had about 600 people coming out. I was in Las Vegas—we had 300 people coming out. Went to Chicago—we had 400 people. So I am sensing that based on that trip and trips that I made to Iowa, New Hampshire, that there is more disconnect and more anger at the establishment—the corporate establishment, the political establishment, the media establishment."

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And of course no one represents the Democratic political establishment more than Clinton. Where she moves cautiously to consolidate support, he speaks with abandon to the visceral concerns of Democratic liberals about some titans of business and finance.

"These people are so greedy, they're so out of touch with reality," he said. "They think they own the world. ... I'm sorry to have to tell them, they live in the United States, they benefit from the United States, we have kids who are hungry in this country. We have people who are working two, three, four jobs, who can't send their kids to college. "Sorry, you're all going to have to pay your fair share of taxes," he asserted. "If my memory is correct, when radical socialist Dwight D. Eisenhower was president, the highest marginal tax rate was something like 90 percent."

Sanders doesn't condemn Clinton for having earned vast sums delivering speeches since leaving the State Department. But he cautions that it could leave her insensitive to the concerns of working-class voters.

"When you hustle money like that, you don't sit in restaurants like this," he said. "You sit in restaurants where you're spending—I don't know what they spend—hundreds of dollars for dinner and so forth. That's the world that you're accustomed to, and that's the world view that you adopt. You're not worrying about a kid three blocks away from here whose mom can't afford to feed him.