Presidential hopeful Bernie Sanders continued to press the case Monday that he had arrived at positions on key issues, including gay rights, long before Hillary Rodham Clinton and that Democratic voters should factor that into their decision on the nomination.

“We live in a tough world, and leadership counts,” the senator from Vermont said during an appearance on “The Rachel Maddow Show” on MSNBC. “It’s great that people evolve and change their minds, and I respect that. … But it is important to stand up when the going is tough. … What the American people and Democrats have to know [is] which candidate historically has had the guts to stand up to powerful people and take difficult decisions.”

Much of Sanders’s discussion with Maddow on Monday focused on the Defense of Marriage Act, a measure signed into law in 1996, when Bill Clinton was in the White House and Sanders was a member of the House of Representatives. The law defined marriage for federal purposes as between one man and one woman and allowed states to refuse to recognize same-sex unions granted under the laws of other states.

Sanders voted against the measure, which he said was discriminatory, but he was on the losing end of a 342-to-67 vote in his chamber.

Hillary Clinton, during an appearance Friday on Maddow’s show, argued that her husband had signed the law as a “defensive action” to shut down momentum at the time toward writing a ban of same-sex marriages into the U.S. constitution. “DOMA was a line that was drawn to prevent going further,” the former secretary of state told Maddow.

On Monday night’s show, Sanders accused Clinton of offering some revisionist history about the “anti-gay legislation” and cited some statements from some prominent gay-rights activists to back him up.

“It bothered me to hear Secretary Clinton saying, ‘Well, you know, DOMA was really to prevent something worse,’” Sanders said. “That just wasn’t true.”

He offered other examples of issues where he had taken a progressive position before Clinton did, including his opposition to the proposed Keystone XL oil pipeline. Opponents have argued that the project poses risks to the environment.

“If you take climate change seriously, and you understand the cataclysmic impact that it will have on this planet, then it is a no-brainer,” Sanders told Maddow. “I have been against that since day one. Everybody knows that.”

Sanders’s tone echoed that of a speech he delivered Saturday night in Iowa as part of a Democratic party dinner that also included addresses from Clinton and former Maryland governor Martin O’Malley, another presidential hopeful. Sanders’s speech, to a crowd of about 6,000 people, was part of a new effort by his campaign to more aggressively draw contrasts with Clinton, the front-runner for the nomination.

Among the other differences Sanders has cited with Clinton include his opposition to the Iraq war, which she supported as a senator from New York, and his long-standing opposition to the pending Trans-Pacific Partnership trade deal, which she only recently came out against.

Sanders’s appearance on Maddow’s show was part of day-long media blitz in New York. The senator also appeared on “The View” and recorded an interview with Charlie Rose that was scheduled to air later Monday night on PBS stations.

While in New York, Sanders also joined about 200 Verizon workers and union members in Times Square who are involved in a contract dispute with their employers.

“We’ve got to stand with unions,” Sanders told Maddow, explaining that “corporations are going to war against their own workers.”