Former hedge-fund executive Tom Steyer isn’t a politician, but he might be one of the most important players in the 2014 midterm elections. According to Federal Election Commission filings from Monday night, Steyer has put $15 million of his personal earnings into the NexGen Climate Action Fund, bringing his total campaign contributions this cycle to $55.9 million, The Guardian reported.

Steyer is now the biggest single donor for the midterms, or at least the biggest donor of  publicly disclosed funds, and is focusing on making climate change an issue at the forefront of the contests.

“We call 2014 a pivotal year for climate,” said Chris Lehane, NextGen’s chief strategist. “If you look around it’s clear that climate has emerged as a top-tier issue.”

Focusing on key elections, Steyer is donating to Democratic senate candidates in Colorado, Iowa, New Hampshire, and Michigan; Democratic gubernatorial candidates in Florida and Pennsylvania; and an Independent gubernatorial candidate in Maine.

The strategy is simple, according to The Guardian.

“NextGen Climate – as well as other environmental groups such as League of Conservation Voters and the Natural Resources Defence Council Action Fund – has run ads ridiculing Republican candidates for denying climate science and accusing them of cozying up to oil and coal companies.”

Lehane said, that while there was data showing a strong concern over climate change in those key states, the issue is important in trying to define the “Republican troglodyte narrative.”

“Climate really for the first time in a long time is being used an offensive issue – a wedge issue and an offensive issue,” said Lehane.

Larry Sabato, a political scientist at the Univesity of Virginia, said the real test of Steyer’s political involvement would be whether or not Democrats retain the Senate.

“If the Democrats shock us and, say, hold onto the Senate 50-50,” said Sabato, “I am sure he will have contributed to Democratic victories in some of those states.”

Regardless of the outcome next Tuesday, Sabato said Steyer would “deserve some credit for elevating the climate issue this time around, and preparing the ground for future races.”