Tensions inside the Republican Party about a proposal to defund Obamacare reached a new level Friday when Sen. Tom Coburn, R-Okla., a lawmaker with unsurpassed credibility in the field of cutting federal spending and limiting the size of government, called the defunding plan “dishonest” and “hype.”

In a phone interview from his home state of Oklahoma, Coburn slammed a dozen fellow Republican senators who have signed a pledge not to vote for any continuing resolution or appropriations bill that funds Obamacare, which is set to go fully into effect on January 1, 2014. “I’d love to defund it,” said Coburn, a physician who has opposed the president’s national health care scheme from the beginning. “I’d be leading the charge if I thought this would work. But it will not work.” (For details on the problems with the defunding plan, see here.)

Coburn’s case against the proposal is simple: Republicans, having failed to win control of the White House and Senate in 2012, do not have the votes to cut off Obamacare funding. Given that, he sees the defunding proposal as not just wrongheaded but also an effort to mislead conservatives across the country who long to see Republicans stop Obamacare. “The worst thing is being dishonest with your base about what you can accomplish, ginning everybody up and then creating disappointment,” Coburn said. “It’s a terribly dangerous and not successful strategy.”

“You’re going to set an expectation among the conservatives in our party that we can achieve something that we’re not able to achieve,” Coburn continued. “It’s not an achievable strategy. It’s creating the false impression that you can do something when you can’t. And it’s dishonest.”

Even though Republicans don’t have the votes to defund Obamacare, they do have the power, if they choose, to bring the government to a halt. Coburn sees that as a disastrous possible result of the plan. “You’re not going to stop the funding, but what you will do is shut down the government,” he said. “Among that group of senators that has been considering this, I was the only one who was here for that,” a reference to the government shutdowns of 1995 and 1996, when Coburn was a member of the House. “The president is never going to sign a bill defunding Obamacare. Do you think he’s going to cave?”

“The strategy that has been laid out is a good way for Republicans to lose the House.”

A push for defunding could also endanger GOP accomplishments in controlling federal spending, Coburn argued. “The one thing that we have achieved is that we have actually cut discretionary spending through sequestration and the Budget Control Act,” he said. “That’s one thing we’ve done great for the country, and you’re going to put that at risk trying to achieve something that is impossible for us to achieve.”

The defunding effort is being led by Sen. Mike Lee, R-Utah, and also includes high-profile supporters Sens. Marco Rubio, R-Fla., Ted Cruz, R-Texas, and Rand Paul, R-Ky. Coburn sees political ambition in the effort. “It’s a denial of reality mixed with a whole bunch of hype to promote groups and individuals who are saying, ‘I’m going to give you hope’ for something that we can’t do,” Coburn said. “The underlying premise is intellectually dishonest. … Creating false expectations and being less than honest about how you’re going to do this is the worst of politics.”

Only once in the conversation did Coburn refer to a fellow lawmaker by name, and that senator was Sen. Lee. “Lee’s answer [to critics] is, ‘Give me a different strategy,’ ” said Coburn. “Well, there isn’t one, because we lost the [election]. I’m getting phone calls from Oklahoma saying, ‘Support Mike Lee,’ and I’m ramming right back: Support him in destroying the Republican party?”