ABC News ' Jonathan Karl reports: Just when it seemed it couldn’t get any worse for Newt Gingrich, a prominent conservative Senator tells him to “keep his mouth shut.” In an interview on ABC’s "Subway Series" with Jonathan Karl to be released Friday morning , Senator Tom Coburn says Gingrich needs “keep his mouth shut” about Paul Ryan’s Medicare plan until he has his own plan to deal with skyrocketing entitlement spending. “If you haven’t put a plan on the table, you need to keep your mouth shut because the problem hasn’t gone away,” Coburn told ABC news in an interview on the Capitol subway. ”You’re elevating yourself by being critical of someone else.” Gingrich has backtracked from his criticism of Ryan’s Medicare plan – on Sunday he called it “right-wing social engineering” – but Coburn sees Gingrich’s remarks as part of a pattern going all the way back to his time as Speaker of the House. “You know, he used to have a little deal in his office that said listen, learn, help and lead. And he rarely followed it. He went the other way. And instead of ready, aim, fire, you got a fire, ready, aim,” Coburn said. ”I think it’s unfortunate for him and unfortunate for the country.” The full interview, including surprising comments from Coburn on tax increases and the fate of the Senate’s so-called Gang of Six, will be released Friday morning.