Why he could: One of the few Republicans on Nader's list, Siebel served as a bundler and fundraiser for the McCain/Palin ticket and hosted fundraisers for Romney in 2012. He's got the money and, based on the few political statements he's made publicly, seems to come from the most conservative wing of the GOP.
Why he probably won't: In his most high profile (and likely, only) political speech to date, he introduced then vice presidential candidate Sarah Palin this way: "Sarah Palin has risen as if from some mythical kingdom of the north. She carries the flag of outrage for the rest of us." There will likely be some desire for an insurgent tea party-esque candidate in 2016, but it's unclear if a political unknown like Siebel would have any real chance.
Why he could: This former hedge fund manager and political moneyman certainly has the ambition and the connections. He's been a fundraiser for Democratic presidential candidates from Walter Mondale to Obama, spoke at the 2012 Democratic National Convention, and has used funneled millions to left-leaning super PACs in efforts to support the environmental causes near and dear to his heart. He has pledged to raise and spend $100 million this year for ads on climate change. Last year, Steyer's name was briefly floated as a possibility to replace Steven Chu as energy secretary. Asked by Bloomberg TV if he'd accept, Steyer said he would.
Why he probably won't: Like almost every candidate on Nader's list, Steyer has never sought elected office previously. Bankrolling the campaigns of candidates who will help spur movement on your issues is one thing. Engaging in a years-long cross-country presidential campaign is another thing entirely. So far, Steyer hasn't come close to signaling he'd be up for that.