Tom Steyer, the top Democratic campaign donor last election cycle, spent more than $74 million trying to elect more environmental candidates to the Senate. He didn't get much for his money. Perhaps that's why he's buying domain names like “Steyer for Senate” as he considers running for office himself.

The billionaire former hedge fund manager is expected to decide in the next few days whether he will run to replace Senator Barbara Boxer, who is retiring from her California seat in 2016. Steyer has also considered running for California governor in 2018's open race.

He should do neither. The climate movement is much better off if he stays the course, supporting environmentally friendly candidates.

The Senate is losing a major environmental advocate in Boxer, and if Steyer runs, Democrats may very well lose their top environmental donor. BuzzFeed reports his super PAC, NextGen Climate Action, will continue no matter what Steyer decides, but it’s not clear whether the operations will remain as large, or whether Steyer intends to sink as much money into 2016. If Steyer runs, green groups could be left short of funds while he self-finances his campaign.

It's understandable that Steyer would rethink how best to influence climate politics: Only a handful of NextGen Climate Action's endorsed candidates won in 2014, with the closest races going to Republicans. Those results notwithstanding, the midterm election was an unprecedented cycle for environmental money, thanks largely to Steyer's donations. For the first time, climate interests had the funding to go head-to-head with the fossil fuel industry. Green groups pushed Democratic candidates in a more hawkish direction and GOP candidates to waver on their conservative positions.

The midterms showed that Steyer’s money alone won’t buy success, but it can help build momentum for action on climate change. Steyer shouldn't abandon his 2014 strategy in favor of personal ambition. The stakes of the 2016 presidential election, which will determine whether President Barack Obama's agenda survives, are much too high for that.