 -- Sen. Bernie Sanders, I-Vermont, said he is concerned by the millions of dollars flowing into the Clinton Foundation at a time when he thinks money plays too strong a role in politics.

“It tells me what is a very serious problem,” Sanders said in an interview with ABC News’ Chief White House Correspondent Jonathan Karl. “It's not just about Hillary Clinton or Bill Clinton. It is about a political system today that is dominated by big money. It's about the Koch brothers being prepared to spend $900 million dollars in the coming election.

“So do I have concerns about the Clinton Foundation and that money? I do,” he added. “But I am concerned about Sheldon Adelson and his billions. I’m concerned about the Koch Brothers and their billions. We're looking at a system where our democracy is being owned by a handful of billionaires.”

Sanders said that “anybody now who is running for office, with few exceptions,” is part of that system.

“I am one of the exceptions," he said. "I am not going to start a super PAC. I’m not going to go around the country talking to millionaires. Now I'm saving my time because they wouldn't give me any money anyhow and that's fine.”

The two-term Vermont senator announced he will run for president in 2016. Sanders, the longest serving independent lawmaker in congressional history, will run as a Democrat in the primaries – the first official challenger to former Secretary of State Hillary Clinton.

“Do I go into this thing as the underdog? Absolutely, no question about it,” he said. “We're going to be heavily outspent, but I think the American people have had enough of establishment politics, i think they want real change i think they want to see a movement which stands up to the billionaire class.”

In the most recent ABC News/Washington Post poll, Sanders was supported for the Democratic presidential nomination by 5 percent of Democrats and Democratic-leaning independents who are registered to vote, trailing behind Clinton by 61 percent.

Sanders, who serves as the top Democrat on the Senate Budget Committee, has advocated for increases to Medicare and Social Security benefits and pushed for ending tax cuts for the wealthy, which he has described as “Robin Hood in reverse.”

“No we're not going to give more tax breaks to billionaires,” he said. “In fact maybe it’s about time that the richest people in this country and the largest corporations started paying their fair share of taxes.”

Sanders, 73, is a self-described Democratic socialist. President Obama even recently joked about what a Sanders campaign would look like.

“Bernie Sanders might run. I like Bernie. Bernie’s an interesting guy. Apparently, some folks want to see a pot-smoking socialist in the White House,” President Obama said at this year’s White House Correspondent’s Dinner. “We could get a third Obama term after all.”

“As a matter of fact, I'm not a pot smoker. I have admittedly some 30, 40 years ago,” Sanders said. “I know people get hung up on the word socialism…I think there are things we can learn from social democratic countries around the world where in fact government does work for ordinary people in a much greater degree than it does in our country.”

Sanders said his first campaign stop will be in New Hampshire this weekend. His formal campaign kick-off will be in May, likely in his home state of Vermont.