- They charged that Donald Trump doesn't believe in climate change
- The latest Republicans to cross party lines to back Hillary Clinton
William D. Ruckelshaus, who was the first EPA administrator under President Richard Nixon and then again the fifth under President Ronald Reagan, and William K. Reilly, the administrator under President George H. W. Bush, said in a joint statement that while Republicans have a history of protecting the environment, Trump "threatens to destroy that legacy of respect for the environment and protection of public health."
"That Trump would call climate change a hoax -- the singular health and environmental threat to the world today -- flies in the face of overwhelming international science," the duo said.
Trump tweeted in 2012, that "The concept of global warming was created by and for the Chinese in order to make U.S. manufacturing non-competitive."
The duo also touted Clinton as someone who "understands that environmental protection is a public health issue" and "recognizes the threat that climate change represents to this country and the rest of the world."
"For us, there is simply no choice in this election," Ruckelshaus and Reilly add. "We Republicans should be shocked, outraged even, at the prospect that all this progress, this legacy will be repudiated and rolled back by Donald Trump."
Both Ruckelshaus and Reilly have been moving away from the Republican party recently.
Ruckelshaus, who was also deputy attorney general in 1973 when he was fired for refusing Nixon's order to dismiss the independent counsel investigating the Watergate break-ins, made news in 2008 when he decided to endorse Obama over Clinton and Republican Sen. John McCain.
Reilly, who has also served as president of the World Wildlife Fund, was appointed by President Barack Obama to co-chair the National Commission on the BP Deepwater Horizon Oil Spill and Offshore Drilling in 2010.