FILE - In this May 5, 2012 file photo, Sen. Sherrod Brown, D-Ohio speaks before a campaign rally for President Barack Obama at Ohio State University in Columbus, Ohio. Big money from outside interests is flowing into the campaign for Ohio's U.S. Senate seat. Nowhere is as much money being spent on a Senate race this year as in Ohio, where liberal Democrat Brown is seeking a second term, his fate to some degree dependent on how well President Barack Obama does in the states tossup presidential contest. (AP Photo/Mark Duncan, File)

WASHINGTON -- Multi-trillion dollar financial institutions continue to get richer, exerting more and more control over both America's economy and its political system. The top 20 largest banks' assets are nearly equal to the nation's gross domestic product.

Now, Sen. Sherrod Brown (D-Ohio), along with unlikely ally Sen. David Vitter (R-La.), is launching an effort to break up the taxpayer-funded party on Wall Street.

"The best example is that 18 years ago, the largest six banks' combined assets were 16 percent of GDP. Today they're 64-65 percent of GDP," Brown said. "So the large banks are getting bigger and bigger, partly because of the financial crisis, partly because of the advantages they have."

The progressive Ohio senator sat down with The Huffington Post in advance of his Thursday speech on the Senate floor to discuss the need to address the "too big to fail" problem and the bipartisan support his work is attracting.

"The system is such that the big banks have far too many advantages, bestowed in part by the marketplace, because investors understand and the market understands that government might in fact bail them out, so there is lower risk for investors, and that means that they can borrow money at a lower cost than anybody else can," Brown said, explaining why small- and mid-sized banks are at a disadvantage.

Brown and Vitter announced on Thursday that they were working together on bipartisan legislation to address this problem.

"I think the fact that Sen. Brown and I are both here on the floor echoing each other's concerns, virtually repeating each other's arguments, is pretty significant," Vitter said Thursday in his Senate floor remarks. "I don't know if we quite define the political spectrum of the United States Senate, but we come pretty darned close. And yet, we absolutely agree about this threat."

In his floor remarks, Brown underscored the urgency -- and the challenge -- in breaking up the biggest banks.

"Just about the only people who will not benefit from reining in the megabanks are a few Wall Street executives," he said.

The two have teamed up in the past on the issue. In January, the Senate passed its bill directing the the Government Accountability Office to examine whether institutions with more than $500 billion in assets enjoy favorable pricing of their debt because of the assumption that the government will always bail them out.

Brown's push received a conservative boost this month from pundit George Will, who wrote that the senator's efforts deserve support from the right.

"By breaking up the biggest banks, conservatives will not be putting asunder what the free market has joined together," he wrote. "Government nurtured these behemoths by weaving an improvident safety net and by practicing crony capitalism. Dismantling them would be a blow against government that has become too big not to fail."

"When the Will column came out, it was pretty interesting," said Brown. "People I've known over the years who have my email address -- I got several emails from people who kind of surprised me that they supported the idea."

Conservative Wall Street Journal columnist Peggy Noonan has urged Republicans to break up the big banks, as has former GOP presidential candidate Jon Huntsman. The idea is also gaining ground with economists and bankers, such as Daniel Tarullo, a governor of the Federal Reserve System, and former Citigroup CEO Sandy Weill.

Brown noted that conservatives and progressives use slightly different arguments and talking points to get to the same conclusion, with conservatives condemning "crony capitalism" and progressives worrying about the corrupting influence of major financial institutions.

"[Will] blamed government for this more than I would, because what he leaves out is the influence of these huge institutions," Brown said. "When bad things happen in society and sometimes the government's complicit, what conservatives usually leave out, in my mind, is the effort [by the big banks] to get the government to be complicit," he said.

In 2010, Brown and then-Sen. Ted Kaufman (D-Del.) also offered an amendment to break up the big banks. Under that measure, no bank would have been allowed to hold more than 10 percent of the total amount of insured deposits, and a limit would have been placed on liabilities of a single bank to 2 percent of GDP.

It failed -- as they expected it would -- but attracted the support of three Republicans. (Vitter did not vote.) Brown said he had no doubt that his latest effort will get more backing in the current Senate, which has Wall Street critics like Elizabeth Warren (D-Mass.).

"I'm not going to mention names, but some who voted [against the 2010 amendment] have come up and said they're going to vote for it. And we just have a different Senate now from 2010," he said, adding, "More and more senators have come to me and said they are looking at this differently now."

Watch Brown's speech on the Senate floor: