His twin passions are at odds. Many of the Republican Party’s elected officials deny that humans are accelerating the warming of the planet, despite the overwhelming scientific evidence. Prominent environmental groups, including the Sierra Club and the Natural Resources Defense Council Action Fund, generally back Democrats, including Hillary Clinton. Yet Mr. Sabin has been a generous donor to the Republican Party for years, contributing more than $500,000 to Republican candidates, committees and other political groups this election cycle.

Even within his party, Mr. Sabin is an outlier: Many other Republicans who believe in climate change have declined to support Mr. Trump. But after backing Jeb Bush early in the primaries, Mr. Sabin threw his wallet behind Mr. Trump and never looked back. He recently donated $100,000 to Trump Victory, the candidate’s joint fund-raising venture with the Republican Party.

To hear Mr. Sabin tell it, a Trump presidency would not be such a threat to environmental concerns. Yes, Mr. Trump has routinely suggested that global warming is not real, has vowed to abolish the Environmental Protection Agency if elected president and said he would walk away from the landmark Paris accord approved last year, in which nearly 200 countries agreed to curb greenhouse gas emissions.

Mr. Sabin, however, brushes that off as election-season bluster. “I don’t think he believes half the things he says,” he said. In meetings with Mr. Trump, he has come away convinced that the candidate is actually a reasonable, well-tempered man who is committed to clean air and clean water. As for Mr. Trump’s proclamations about the E.P.A. and the Paris agreement, Mr. Sabin is dismissive, arguing that such actions wouldn’t get through Congress. “There are good checks and balances,” Mr. Sabin said. “He won’t be able to do whatever he wants.”

The Trump campaign did not respond to a request for comment.

As much as he supports the Republican ticket, Mr. Sabin is equally motivated by his loathing for Mrs. Clinton, whom he derides as untrustworthy, unethical and unfit for office. In front of his mansion, in an organic garden that features kale, blueberries and Swiss chard, Mr. Sabin has erected several “Hillary for Prison” yard signs. Last year, after the signs disappeared in the middle of the night, Mr. Sabin placed them on stilts and surrounded them with a 6,600-volt electrified fence.