The White House’s senior adviser on energy and climate change stepped down last week after being denied a full security clearance for smoking marijuana about five years ago. Now he is speaking his mind about the Paris climate agreement that President Trump has disavowed.

“I’m going to say something controversial,” the former adviser, George David Banks , said in an interview. “The Paris agreement is a good Republican agreement. It’s everything the Bush administration wanted.”

Mr. Banks stood by Mr. Trump’s decision last summer to withdraw the United States from the global accord, despite having urged him behind the scenes to remain in. Since then, a large part of his work as the White House adviser on international energy issues has been to quietly seek ways that the United States might rejoin the deal.

That came to an abrupt end last week when Mr. Banks resigned after being told he would not be granted a full security clearance. In a wide-ranging interview days after leaving his position, Mr. Banks spoke about the surprise of being told that the three or four times he had smoked marijuana between 2009 and 2013, which he had self-reported to the F.B.I. in April 2017, were the reason for the security rejection.