An outspoken conservative lawmaker recently challenged Senate Republican Leader Mitch McConnell (Ky.) at a closed-door meeting, saying there is a GOP “leadership vacuum” in the upper chamber, according to sources.

Sen. Tom Coburn (R-Okla.) summed up the frustration of several colleagues at a gathering of the Republican Steering Committee. He chastised Sens. Ted Cruz (R-Texas) and Mike Lee (R-Utah) for how they have waged their aggressive push to defund ObamaCare.

Their rhetoric, Coburn said, has been used in television and radio ads attacking other Republican senators.

“He said to Cruz and Lee, ‘Don’t pretend to be naïve. You know outside groups are using what you’re doing as ammo against your colleagues,’ ” a Republican who attended the meeting said.

{mosads}Coburn also told McConnell that he had allowed the situation to spin out of control.

“He said to McConnell, ‘This has happened because there’s a leadership vacuum,’ ” the Republican source said.

A second Republican who attended the meeting confirmed the exchange.

Coburn declined to talk about his private conversation.

“I don’t comment on anything said in conferences,” he said.

Another Republican senator told The Hill that McConnell has paid too much deference to Lee and Cruz.

“What gets me is he’ll look at 46 [Republican] senators and say, ‘What do Mike and Ted want to do?’ What are we, chopped liver?” the lawmaker said.

But the senator expressed sympathy for McConnell, as well, because he’s facing a conservative primary challenger.

“I wouldn’t want to be in Mitch’s shoes. He and [Speaker John] Boehner [R-Ohio] are in such a tough spot,” the Republican legislator said.

Many GOP senators think they’ve become trapped in a bad political position, and worry it could hamper their chances to win back control of the Senate.

Recent polls showed that most Americans would blame the GOP for a government shutdown.

Few Republican senators thought it would be possible to defund or delay ObamaCare by linking the issue to a stopgap spending measure.

Now much of the government has been shuttered since Tuesday and Democrats continue to refuse to negotiate any changes to the Affordable Care Act.

Many Republicans think they have a built-in advantage in the 2014 midterm election because the president’s party usually fares poorly halfway through his second term. Moreover, Democrats must defend many more competitive seats than Republicans.

Several GOP senators now worry they’re “squandering” a strong position in a messy battle that is unlikely to yield a policy victory.

They are frustrated that Cruz, who has served in the Senate since January, is driving the debate and does not appear to have a viable endgame strategy. And some Republican senators believe they are on a politically suicidal ride, with Cruz and Boehner at the wheel.

Yet, others on both the left and the right believe Cruz has done well.

MSNBC host Chris Matthews, a former Democratic staffer, said this week, “I think Ted Cruz is brilliant. I think the president’s met his match in this guy. He set this thing up months ago.”

Senate Majority Leader Harry Reid (D-Nev.) said the crisis could be solved if Boehner puts the Senate-passed spending bill up for a vote on the House floor.

Boehner has been reluctant to do so because doesn’t want to alienate a group of House conservatives, some of whom have openly challenged the Speaker’s leadership.

These House conservatives, in turn, appear to be taking their cues from Cruz and Lee.

The dynamic was made clear earlier in the week after House conservatives embraced Cruz’s and Lee’s strategy of passing piecemeal bills to continue government funding. Boehner signed onto the game plan after the senators persuaded House conservatives to adopt it.

Senate Republicans subsequently urged Senate Democrats at least to fund departments not involved in the implementation of ObamaCare.

But senior Senate Republicans are exasperated that the entire party appears to be ultimately taking its lead from two junior members.

A Senate GOP aide defended McConnell, saying the minority leader has played a behind-the-scenes role. The GOP leader is often seen speaking one-on-one with colleagues during votes.

McConnell’s allies tried to rein in Cruz and Lee ahead of the shutdown. That wouldn’t have happened, according to conservative GOP strategists, without the green light from McConnell.

Sen. Richard Burr (R-N.C.) called the strategy of threatening a government shutdown unless Democrats defunded ObamaCare “the dumbest idea I’ve ever heard.”

Sen. Mike Johanns (R-Neb.) suggested last month that Cruz was primarily driven by presidential ambitions and the desire to build up his email list of potential supporters. 

Another GOP aide said McConnell has taken a relatively low profile in the government shutdown fight because he does not want to step on Boehner’s leadership.

“It’s a matter of not wanting to box in House Republicans and wanting to give them maximum flexibility,” the senior aide said.

Some Republicans claim the media has exaggerated the political damage their party will suffer compared to the Democrats.

While most voters may view the GOP as primarily responsible for the shutdown, the issue will likely fade once funding is restored, they argue.

The votes that vulnerable Democrats such as Sens. Mark Pryor (Ark.) and Mark Begich (Alaska) cast against defunding and delaying the healthcare law will fuel campaign ads next year, they say.

“I’m sure things will get uncomfortable for red-state Democrats,” the GOP aide said Tuesday. “The vote Democrats took last night was a really nasty vote.”

The staffer was referring to the Senate vote to table House legislation that would have funded the government while preventing congressional lawmakers and staff members from taking federal subsidies after entering healthcare exchanges. 

The modified stopgap bill also would have delayed the individual mandate, a core component of ObamaCare.

The GOP aide added that Senate Republicans are “united on protecting the historic gains they’ve made in reducing spending and locking in permanent tax relief. [McConnell has] led several meetings over the course of the CR/debt-ceiling debate, and his members have a singular focus on keeping their commitment to the American people to reduce spending …”