According to a Gingrich mistress. From the Village Voice:
"If you believe Newt Gingrich's former mistress Anne Manning, the Speaker has for decades relied on the blowjob as the sex act with built-in plausible deniability. Referring to her first date in 1977 with Gingrich, Manning told Vanity Fair in 1995: "We had oral sex. He prefers that modus operandi because then he can say, 'I never slept with her."'