BURLINGTON, Iowa >> Democratic presidential candidate Bernie Sanders ramped up his criticism of Hillary Clinton’s ties to Wall Street and history of evolving on issues, seeking an upset victory in Monday’s first-in-the-nation Iowa caucuses.

Speaking at a Thursday evening rally in Burlington, Iowa, Sanders cast himself as a legislator steeped in principle, pointing to his opposition to the Iraq war, the Trans-Pacific Partnership trade deal, the Keystone pipeline and the 1996 Defense of Marriage Act, which was signed into law by President Bill Clinton, who later said he regretted the decision.

“Check the record, find out where my opponent was on all of these issues,” Sanders said. “It is great to be against the war after you vote for the war. It is great to be for gay rights after you insult the entire gay community by supporting DOMA.”

“It is great to finally — kicking and screaming — come out against the TPP. But where were you on all of the other trade agreements?” Sanders asked, adding: “What leadership means is not simply following the majority.”

The tough talk came as Clinton has scrutinized Sanders’ record on gun control, calling him a “pretty reliable vote for the gun lobby” and accused him of planning a major tax increase to pay for a single-payer health care system through Medicare, arguing it would undermine President Barack Obama’s health care law.

Clinton spokeswoman Christina Reynolds said it was “ironic that Senator Sanders is preaching consistency on the very day he flip-flopped on his position on a bill to end immunity for gun makers and dealers or that he’s touting his positive campaign while simultaneously ramping up the attacks.” Sanders is formally backing a bill to repeal a 2005 law he supported protecting the gun industry from lawsuits.

“Hillary Clinton would rather spend her time talking to Iowans about how she’ll help make a difference in their lives,” Reynolds said.

The campaigns have had feisty exchanges as Iowa’s leadoff contest nears. A new Clinton ad says she would build upon the health care law, “not start over,” and defend Planned Parenthood, “not attack it,” messages that reinforce charges she has made against Sanders. In a statement, Sanders said the ad “completely distorts my record.”

Sanders is trying to upset Clinton in Iowa, where her advantage has narrowed in recent weeks, and then claim victory in New Hampshire, where polls show him with a steady lead in the Feb. 9 primary. Traveling by bus through Iowa, the senator predicted a win in Iowa if the turnout was large but warned if not, “we’re going to be struggling.”

Honing in on Wall Street, Sanders launched a new television ad critical of Goldman Sachs’ role in the financial meltdown and its payment of speaking fees and campaign contributions. The 30-second ad, which will begin airing Friday, makes no mention of Clinton, who received more than $600,000 in speaking fees from the Wall Street firm.

“As long as Washington is bought and paid for, we can’t build an economy that works for people,” the narrator says.

Sanders only appears at the end of the ad to approve the message. But his argument seeks to capitalize on concerns by Democrats that Wall Street has become too influential in the nation’s economy and political system.

The so-called “democratic socialist” vows to break up the country’s biggest financial firms within a year if he’s elected president and limit banking fees placed on consumers. He pointed to Clinton’s Goldman Sachs speaking fees during the last presidential debate and reminded supporters this week that Clinton took a break from the Iowa trail to raise money at a Philadelphia investment firm.

Clinton argues that her financial regulation proposals would do more to crack down on industry abuses and rein in risky behavior within the shadow banking sector.

“We’ve got some work to do and I want to do it by getting the wealthy to pay their fair share for the benefits they have enjoyed by being Americans,” Clinton told several hundred voters gathered at a middle school in Newton, Iowa.

Responding to the ad, Clinton’s campaign said Sanders was shifting into attack mode and breaking his pledge not to run negative advertising.

“This last-minute sneak attack from the Sanders campaign is clearly meant to plaster the Iowa airwaves in the days before the caucus with negative ads slamming Hillary Clinton, without giving our campaign time to respond,” said Matt Paul, Clinton’s Iowa director. “It’s a cynical political ploy.”

It came on a day when Sanders’ campaign conducted damage control in Nevada and released the senator’s medical records, something he had vowed to do before the Iowa caucus.

Leaders of the powerful Culinary Workers Union in Las Vegas — which remains neutral in the race — condemned Sanders’ campaign staffers who falsely claimed an affiliation with the union as a way to gain access to its members at casino employee dining rooms. Sanders campaign manager Jeff Weaver said the campaign reminded staffers it was inappropriate “and that they should not do it again.”

Earlier, Sanders’ campaign distributed a one-page letter from the senator’s doctor, who declared the candidate to be in “overall very good health.”

It said Sanders had been treated in the past for ailments like gout, high cholesterol and laryngitis. He underwent hernia surgery earlier this year but is in good health, his doctor said.

“You are in overall very good health and active in your professional work, and recreational lifestyle without limitation,” wrote Sanders’ longtime doctor, Brian Monahan, the attending physician of the U.S. Congress.

If elected, Sanders would be the oldest president to assume office, surpassing Ronald Reagan who was 69 when he entered the White House. Sanders is about six years older than Clinton, who released her medical records in July. Her doctor said at the time she was in “excellent physical condition.”

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Associated Press writer Lisa Lerer contributed to this report from Newton, Iowa.

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