Washington (CNN) The lead plaintiff in a landmark Supreme Court case that legalized same-sex marriage nationwide said Thursday he doesn't believe President Donald Trump's stated belief that the issue is settled.

James Obergefell appeared on CNN's "New Day" one day after Justice Anthony Kennedy announced his retirement. Kennedy was the decisive swing vote in the 2015 Obergefell v. Hodges case, and although Trump said in 2016 that same-sex marriage was a settled issue, Kennedy's retirement has raised questions about whether a Trump-appointed justice could overturn same-sex marriage as a legal right.

"He says one thing, one day, and says the exact opposite the next day," Obergefell told CNN's Erica Hill.

"I have to believe that there are people behind him pushing him that will force this issue and bring this back up for a vote, or for a hearing, and that really concerns me," he added.

Asked about same-sex marriage in early 2016, Trump said the issue has "been ruled up" but also said he would be "very strong on putting certain judges on the bench that I think maybe could change things." He indicated after the election that he's "fine" with the high court's opinion legalizing same-sex marriage and called it "settled." Trump has also told CNN's Jake Tapper on "State of the Union" that he is for "traditional marriage."

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