U.S. Republican presidential candidate and former Massachusetts Gov. Mitt Romney and vice presidential hopeful Wisconsin Rep. Paul Ryan greet supporters during a campaign rally at Waukesha County Expo Center in Waukesha, Wis., August 12, 2012. - 

Kai Ryssdal: There is, as we all know, just one president of the United States. But right now, Paul Ryan-Mitt Romney are selling themselves on the campaign trail as what you could call team "fiscal responsibility." And that got us wondering about companies with two CEOs and how well they actually work.

Marketplace's Shereen Marisol Meraji has that story.

Shereen Marisol Meraji: Four years ago, now, President Obama, introduced Joe Biden as his running mate like this:

Barack Obama: Let me introduce to you the next president...

He corrected himself, a moment later. Just a couple of days ago Gov. Romney made a similar gaffe.

Mitt Romney: Join me in welcoming me the next president of the United States, Paul Ryan!

Mistakes aside, we are all aware that, constitutionally, there can only be one president. Co-CEOs of a business share power -- legally -- either by terms laid out after a merger or they co-own the company.

Stephen Ferris: In other types of organizations, like politics, it's much more functional or informal but can be equally effective.

Stephen Ferris is a finance professor. He did a study about co-Ceos. Ferris tracked 120 businesses over a 20 year period -- those run by two heads had stronger returns. The key to success is what he calls, complimentarity -- educational backgrounds and expertise that are different.

Ferris: Some of the co-CEOs would maybe have primary responsibility, say for manufacturing and engineering and product design, whereas the other CEO might have more responsibility for marketing and distribution.

But Ferris is a finance professor. I called presidential historian Richard Norton Smith to see if there's any proof that power sharing works on a presidential level. He points to the 36th vice president of the United States, Richard Nixon. He was Eisenhower's VP.

Richard Norton Smith: It was a genuine balance of talents, experiences, weaknesses.

Since Nixon, Smith says we've had a few of what he calls "deputy presidents" --  Walter Mondale, Dick Cheney, and Al Gore. But, he says choosing a vice presidential running mate is less about co-running a country and more about co-running a campaign where the return on investment is getting elected.

I'm Shereen Marisol Meraji for Marketplace.

Follow Shereen Marisol Meraji at @RadioMirage