Sen. Bernie Sanders, who is competing against Hillary Clinton for the Democratic presidential nomination and is closing in on her in some early state polls, made a beeline to a bank of cameras stationed outside a closed-door meeting where Clinton was meeting with Democratic lawmakers on Tuesday.

The Independent senator from Vermont was there to talk about the differences between his and Clinton's positions on key issues, although when asked about ethics rules prohibiting campaigning in the Senate, he insisted he wasn't committing any violations.

"I am not campaigning here," he answered reporters. "You are asking me questions."

But Sanders spent the bulk of the time laying out his views on key issues and comparing them with Clinton's position, or lack of one, on matters ranging from the recently passed trade negotiation deal, the Keystone pipeline project, raising the minimum wage, anti-terrorism surveillance laws and free college tuition.

"I believe if we are going to rebuild the middle class, we need to make public colleges and universities tuition-free and pay-free, through a transaction tax on Wall Street speculators," said Sanders, a self-declared socialist. "The secretary's position, I think, is unclear on that."

Sanders said he differs with Clinton on regulating Wall Street — he wants to break up the big banks, while Clinton "does not agree" with this idea.

Clinton has refrained from stating her position on other critical issues, Sanders said, including whether to approve the Keystone pipeline.

"I don't believe we should be excavating and transporting some of the dirtiest fuel on this planet," Sanders said. "I think Secretary Clinton has not been clear on her view on that issue."

Sanders also touted his 2002 vote against the Iraq war. Clinton voted in favor of the war, although recently she said her vote was "a mistake."

Sanders said he has known Clinton for 25 years.

"I like her and I respect her and I hope we can run a campaign where we can express the difference that we have and do it in a way that is straightforward," Sanders said. "It's not necessary for people to dislike each other, to attack each other."