(Photo : (Photo by Mario Tama/Getty Images))
RFK Jr. was a senior attorney for the Natural Resources Defense Council for 28 years before stepping down in 2014.

Several former colleagues of Robert F. Kennedy Jr. at the Natural Resources Defense Council (NRDC) and other national environmental organizations are calling on him to withdraw from the presidential race. 

Full-page advertisements, sponsored by the NRDC's political wing, are schedule to appear in newspapers in six swing states on Sunday.

"Earth to RFK Jr. ... Drop Out," says the ad.

A dozen national environmental organizations have issued an open letter denouncing Kennedy as a "dangerous conspiracy theorist and a science denier," promoting "toxic beliefs" regarding vaccines and climate change. 

The critics argue that the independent candidate cannot win the presidency, but could divert votes away from President Biden, potentially aiding former President Donald Trump, who has dismissed climate change as a hoax and pledged to dismantle environmental laws and policies, noted the New York Times.

"A vote for RFK Jr. is a vote to destroy that progress and put Trump back in the White House," says the newspaper ad that will run in Georgia, North Carolina, Nevada, Michigan, Wisconsin and Pennsylvania. 

Signatories, including John Hamilton Adams, a co-founder of the Natural Resources Defense Council who hired Kennedy in the 1980s, along with past presidents and the group's current president, implore Kennedy to "honor our planet: drop out."

In a telephone interview with the Times, Kennedy pushed back against the idea that he could bring Trump back to the White House. 

"President Biden does not need my help to lose to Donald Trump," he countered.