Two former Republican EPA chiefs endorsed Hillary Clinton for president on Tuesday. William D. Ruckelshaus, who ran the agency under Richard Nixon and again under Ronald Reagan, and William K. Reilly, who was EPA administrator for George H. W. Bush, argue that Donald Trump would roll back decades of environmental progress made under both Republican and Democratic presidents.

“Donald Trump has shown a profound ignorance of science and of the public health issues embodied in our environmental laws,” Ruckelshaus and Reilly write in a joint statement. They express particular disgust with Trump’s climate science denial and opposition to climate action, even though those remain common positions among leading Republicans.

Of course, Republican EPA chiefs often come from the moderate wing of the party. George W. Bush’s first EPA administrator, Christine Todd Whitman, said in March that she would probably support Clinton over Trump. Ruckelshaus has already crossed the aisle once before, endorsing Barack Obama for president in 2008.

Still, coming just a day after 50 Republican senior national security officials published a letter saying they will not vote for Trump, Ruckelshaus and Reilly’s statement reflects a growing rejection of their candidate by the party’s own governing class.

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