The actor stars in The Best Man as a senator who is driven to sin and corruption in pursuit of power.
Discussing the play with The AP, McCormack joked that Will & Grace fans are often shocked when they come to see The Best Man.
"People come in going, 'Oh, there's that nice guy from Will & Grace', and within about 20 minutes, they're like, 'Oh. I. Hate. That. Guy'," the star joked, adding: "It's a bit like a betrayal."
McCormack further explained that his Best Man character is "Don Draper-meets-Rick Santorum" and represents a dark side of the American dream.
"He's a monster, but he's an attractive monster. No sweater vests, though. That is out," McCormack joked in reference to Santorum's now-famous attire. "My character is the kind of guy who shoots first and asks questions later."
Gore Vidal's The Best Man is currently playing at the Gerald Schoenfeld Theatre in New York City.
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Watch a clip of Eric McCormack in Gore Vidal's The Best Man below: