(CNN) Sen. Bernie Sanders on Sunday denied an accusation made by Hillary Clinton last week that the Vermont senator's delayed endorsement in 2016 hurt her Democratic presidential candidacy, saying that he did everything he could to get the former secretary of state elected president.

"I'm sorry that Hillary Clinton is rerunning 2016," Sanders said in an interview with Iowa Press that aired Sunday. "I could take out a letter from Hillary Clinton saying, 'Thank you Bernie for working so hard to try to make me the President of the United States.' "

Sanders' rebuttal comes after Clinton talked to Howard Stern Wednesday in a radio interview in which she spoke to questions of whether the Democratic Party did enough to come together during the last presidential election cycle.

"I don't hate anybody," Clinton said when Stern asked about Sanders and his 2016 Democratic primary campaign. But Clinton did not hesitate to point out that she believed Sanders' delayed endorsement hurt her campaign. "He hurt me there's no doubt about it, and I hope he doesn't do it again to whoever gets the nomination. Once is enough," Clinton said.

Sanders said Sunday that he "worked as hard as humanly possible" once Clinton was the Democratic nominee. "We did dozens and dozens of rallies around this country," he added.

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