On January 17, 2019, Weld rejoined the Republican Party, increasing speculation that he would run for president. On February 14, 2019, Weld announced that he was launching a presidential exploratory committee for the 2020 Republican primary, against incumbent Republican President Donald Trump. Appearing on Bloomberg News, Weld suggested that he could beat Trump in 2020 with help from independent voters. He accused Trump on CNN the same weekend of having "showed contempt for the American people." Weld challenged Trump on the issue of climate disruption, saying that he had made no effort to combat the effects of global warming. "We've got the polar ice cap that's going to melt with devastating consequences if we don’t get carbon out of the atmosphere," Weld told America's Newsroom, noting that he would plan ahead for an "environmental catastrophe."