BURLINGTON, Iowa— Seeing the opportunity for a surprise victory in the opening contest of the Democratic presidential campaign, Bernie Sanders has set his sights squarely on Hillary Clinton just days before the Iowa caucuses.

At the end of the first day of Sanders’ final bus tour through Iowa, the Vermont senator unleashed a barrage of contrast points with Clinton, going after his Democratic primary opponent on everything from her delayed opposition to the Trans-Pacific Partnership to her initial support for the Defense of Marriage Act.

“I would ask you, check the record,” Sanders implored the crowd of over 850 supporters at a evening rally at the Burlington Memorial Auditorium. “Find out where my opponent was on all of these issues.”

Without mentioning Clinton’s name, Sanders rattled off a number of issues important to many progressive Democrats, all while calling Clinton’s leadership and consistency into question.

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“It is great to be against the [Iraq] war after you vote for the war,” said Sanders, referring to then Sen. Clinton’s 2002 vote for the war in Iraq.

“It is great to be for gay rights, after you insult the entire gay community by supporting DOMA,” Sanders continued, highlighting President Bill Clinton’s signing of DOMA and Hillary Clinton’s support of the bill at the time.

In perhaps his most pointed critique, Sanders then asserted that Clinton only came out against the TPP “kicking and screaming,” but then asked: “Where were you on all of the other trade agreements?”

Sanders also revived criticism of Clinton’s perceived delayed opposition to the Keystone XL Pipeline as well as her having given paid speeches for Goldman Sachs.

This focused line of attacks comes just a few days before the Iowa caucuses, where polls show a tight race between the two candidates.

“I would say at this moment, the Iowa caucuses are a toss-up,” Sanders told an overflow room at an event Friday in Fairfield, Iowa.

Sanders, who has boasted of never running a negative television ad in his life and keeping the campaign centered on issues, has now been accused by the Clinton campaign of turning negative.

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One senior strategist for the Clinton campaign asserted Friday on CNN that Sanders was running the “most negative campaign of any Democratic presidential candidate…in a presidential primary season.”

The Clinton camp points to a new Sanders campaign video titled “The Problem,” which talks about Washington, D.C. and the economy being “rigged by Wall Street” via campaign contributions and speaking fees.

NBC’s Andrea Mitchell asked Sanders on Thursday if he believed it was a negative ad.

“Does it mention Hillary Clinton? Does it have any image of Hillary Clinton?” Sanders responded.

Speaking later in Burlington, Sanders explained why he is bringing up all of these contrasting points with Clinton at this point.

“So what all of this is about, is that what leadership means is not simply following the majority,” the candidate from Vermont said.

Sanders concluded this thought by adding that his record is “boringly consistent” to cheers from the packed audience.

This article originally appeared on NBCNews.com.