Tom Steyer has picked a lot a fights recently.
The billionaire former hedge fund manager has continued his high-profile campaign against climate change this year, using his NextGen Climate group to create attack ads targeting conservative industrialists Charles and , Republican Sen. Marco Rubio, and Terri Lynn Land, the GOP Senate candidate in Michigan.
Steyer continued his digs at the Koch brothers--prominent supporters of conservative politicians--by challenging them to a debate on climate change and energy policy.
"We are using our resources to promote an interest that we believe will help our children, while they appear to be promoting an agenda that will benefit their economic self-interest," Steyer said when issuing the challenge April 25. "We deal in science, while they are involved in efforts to attack science."
Steyer then issued this ad after not hearing back.
A spokesman for the Kochs said they never got a direct invitation and that the "Crickets" ad was misleading.
"For the record, NextGen never contacted us directly to invite Charles and David Koch to debate in the first place," said Rob Tappan of Koch Industries, noting the invite was technically an ad in Politico. "It was a publicity stunt. We responded and declined the invitation to debate Mr. Steyer when the Wichita Eagle…contacted us."
Steyer has also criticized Rubio—a potential 2016 presidential candidate—following the Florida senator's recent remarks on how climate change laws hurt the the economy.
NextGen Climate launched a new media campaign called "Planet Rubio" to point out "the absurdity of denying the scientific consensus on man-made climate change," according to an email announcing the effort.
A spokesman for Rubio declined to comment, but referred readers to remarks made on CNBC recently regarding climate change.
"I actually said the same thing I said before," Rubio noted on air. "I do not believe these laws will do anything about it. And I'm not going to help destroy America's economy."
Steyer's group has also been targeting Land's Senate campaign because of what it characterizes as Koch support of her candidacy.
Koch-funded political advocacy group Americans for Prosperity bankrolled ads critical of Land's opponent, Democrat Gary Peters. But the group does not explicitly endorse candidates.
The Land campaign did not respond to a request for comment.
The moves come as Steyer continues to funnel money to Democrats. The latest is a fundraiser at his San Francisco home on May 28 for the Democratic National Committee featuring Vice President Joe Biden. Steyer has previously hosted President Barack Obama and Senator Harry Reid at similar events.
More is likely in store. Steyer has said he could spend $100 million—$50 million personally and $50 million from others—in 2014 based on candidates' views on the Keystone XL pipeline and other climate-change issues.
A spokesman for Steyer did not immediately respond to a request for comment on this story. Steyer told CNBC.com in December that "climate is the defining issue of our generation."