They turned to filmmaker Jay Roach, whose schizophrenic career as a director of farcical comedies ("Austin Powers," ''Meet the Parents") and acclaimed HBO based-on-real-life political dramas ("Recount," ''Game Change") made him a natural choice.
With little more than the outline of a promising concept that would match the two comedians mano-a-mano, the movie was green lit with a production schedule and a release date that would lend the obvious tie-in to the 2012 presidential election. The script by Chris Henchy and Shawn Harwell came later.
"Their chemistry is amazing but it's almost unlikely," says Roach. "They couldn't be more different in their physicality, their attitudes. Will's so instantly accessible and then there's other things going on. Zach is instantly inaccessible and then there's other things going on."
From the start, it was conceived as a platform for Seth Galifianakis, the comedian's fictional brother character, a sometimes racist Southern effeminate with a mustache (as opposed to Galifianakis' usual beard). In the film, Galifianakis plays a version of the character named Marty Huggins.
Knowing the setting was North Carolina, Ferrell found inspiration in former senator John Edwards, albeit with shades of his President George W. Bush impression from "SNL."
Part of the thrill of seeing Galifianakis and Ferrell square off is that they seem to have an offbeat rhythm set to the same metronome. Though they come from different sides of the comedy spectrum (Galifianakis from stand-up, Ferrell from improv), they share an uncommon ability for stretching awkwardness beyond the threshold of most.
"I have learned as a stand-up it's much better for acting to go the way of someone that has improv training and pay attention to that," says Galifianakis. "It is much better if it's a group effort. I always say less is more, for me. I don't need to say a lot of things. I don't want to say a lot of things. (in a whisper) I don't want to work."
The two have worked together a few other times, including a memorable video for Galifianakis' beloved Web series "Between Two Ferns" and a tour for Funny Or Die (the website Ferrell co-founded) in 2008 that played for college audiences of thousands. In Ferrell's opening, Galifianakis and other comics on the tour played ninjas attacking him.
"It was like a rock show," Galifianakis recalls. "It was like being in Toto."
"Or DeBarge," chimes Ferrell.
"DeBarge," Galifianakis solemnly nods in agreement.