Former Vice President Al Gore criticized President Trump on Tuesday night for “isolating himself” on the issue of climate change by surrounding himself with a “rogue’s gallery of climate deniers.”

Gore expressed regret that Trump has not pursued policies to tackle climate change, after previously being hopeful that the president would do more.

“He has in some ways isolated himself from the overwhelming majority of public opinion in the country,” Gore said in a CNN town hall focused on climate change and hosted by Anderson Cooper.

“They are tongue-tied because the truth about the climate crisis is still inconvenient for the large carbon polluters, and they unfortunately have a lot of influence over this administration,” Gore added. “He has surrounded himself with a rogue’s gallery of climate deniers.”

Earlier this year, Gore spoke with Trump in a failed bid to persuade the president to remain in the Paris climate agreement, an international accord signed by 195 nations that pledged to cut greenhouse gas emissions.

Trump announced in June that he would withdraw the U.S. from the accord. Gore said he was surprised Trump chose that course.

“I did feel there was a real chance he might come to his senses and stay in the Paris Agreement,” Gore said. “We [the U.S.] have a real chance of meeting the terms of the agreement regardless of what Trump does,” he added, citing pledges made by governors and mayors to reduce emissions.