Story highlights Sanders challenges Clinton to address issues he talks about in an interview with CNN

"Now is Hillary Clinton going to say that?" he asks after outlining part of his populist platform

Senator realizes he knocked Clinton and later states, "I am not here to attack Hillary"

Sanders is openly toying with a presidential run and will be in Iowa this week

Bernie Sanders wants you to know he's talking about the issues that Hillary Clinton is not.

At the end of a winding answer to a question about how he differs from Hillary Clinton, the U.S. senator challenged the former secretary of state.

"If we do not get our act together to come up with public policy which expands the middle class, if we don't overturn Citizens United, if we don't move to public funding of elections, we are going to live in an oligarchic form of society," Sanders said. "Now is Hillary Clinton going to say that?"

It was a candid moment and the closest the senator -- who is most known for being an independent who regularly targets Wall Street and money in politics -- came to a direct knock on Clinton's possible run at the presidency during an interview with CNN before his upcoming trip to Iowa. His comment about Citizens United referred to a 2010 U.S. Supreme Court decision that opened the floodgates for outside money in politics and ballooned the amount spent on campaigns.

It was also something that the Vermont senator quickly realized didn't match his statement, "I am not here to attack Hillary."

"I know Hillary, I respect Hillary Clinton," Sanders said. "I knew her when she was first lady, I certainly knew her as a colleague in the Senate. "I don't know if Secretary Clinton is running for president and I have no idea what she is going to be campaigning on. But I do know what I believe and what I will be speaking about."

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Sanders, who caucuses with Democrats, is trying to thread a needle.

He is little known outside liberal circles, yet the two-term senator is openly considering a run at the presidency in 2016. He is making the trip to Iowa this weekend and will speak in New Hampshire in a few weeks.

He is floating the idea of a run with journalists and political operatives and saying things like,"If I choose to run."

Yet Sanders doesn't want to openly talk about Clinton and says he would rather focus on his views on the "political," "economic" and "media" establishments. He is attacking Clinton, something most Democrats aren't doing, but trying to say he isn't.

Correct the Record, a pro-Clinton communications group, took issue with the idea that Clinton didn't address the issues Sanders had been addressing.

"Senator Sanders has a good point -- the American people always want a campaign that includes a spirited dialogue about the issues," said Adrienne Elrod, the group's communications director. "But Hillary has spent her entire life turning talk into action, putting policies in place to make lives better for all Americans."

Coincidentally, Sanders' trip to Iowa this weekend comes at the same time Clinton will be making her first trip to the critical presidential caucus state in six years.

Clinton, who is herself openly considering a run at the presidency, will be the headliner at the politically important Tom Harkin Steak Fry. Thousands of guests expect to listen to her speak, flip steaks and honor Harkin, the liberal senator who is retiring after 2014.

Sanders, on the other hand, will not be at the steak fry. He will start the weekend with a speech at the Fighting Bob Fest, an annual meeting of progressive speakers in Wisconsin that honors Robert "Fighting Bob" La Follette, a longtime liberal senator from the Badger State.

Following his speech, where aides expect him to articulate his liberal platform, Sanders will travel to Iowa for town hall-style events in Dubuque, Waterloo and Des Moines, respectively.

For Sanders, who has done hundreds of town hall events in his home state, the Iowa events comes with pros and cons.

Primarily, they allow the senator to get his name out there and gauge interest in him as a candidate.

"I want to find out what kind of support there is for a progressive agenda which takes to the needs of a collapsing middle class and the growing wealth and income inequality America," Sanders said. "It is easy to give a good speech and get applause, it is not so easy to put together a grassroots movement of people who are prepared to fight for change."

But they will also offer a glimpse of his uphill climb. While Sanders speaks to small town halls, Clinton will likely be fawned over by thousands of supporters at the most political event of the year in Iowa.

Sanders was clear to point out that he does know Harkin, the organizer of the steak fry, "very well" and was invited "a couple of years ago to be the guest."

But Sanders sees a bigger positive for him in attending small events and offering a stark alternative to Clinton.

"I don't think anybody believes that anointment is a good idea, that anybody is quote unquote entitled to a nomination or any other position," Sanders said. "I think what people in Iowa and through the country want to hear is a vigorous debate about the most important issues which impact their lives. It is not to say to somebody, 'Oh, thank you, you are going to be anointed as our candidate.'"