Republican Sens. John McCain (Ariz.) and Lindsey Graham (S.C.) sent a letter to the Pentagon tonight asking Defense Department officials to evaluate the consequences for the military if the Joint Committee on Deficit Reduction fails.

The super committee has 20 days left to identify $1.2 trillion in savings over the next 10 years, but it is struggling to find a bipartisan agreement that includes both entitlement reform and revenues. Should it fail, 10 years of across-the-board cuts affecting defense spending, domestic discretionary spending and Medicare would kick in.

The two Senators have expressed serious concerns over the effects that deep defense cuts would have on American security if the super committee fails. In the letter addressed to Defense Secretary Leon Panetta, they said the automatic cuts were “draconian” and could lead to a “hollow military.” They then asked for a “frank and honest assessment describing in concrete terms what defense spending cuts of this magnitude would entail.”

McCain, the ranking member on the Senate Armed Services Committee, and Senate Minority Whip Jon Kyl (R-Ariz.), who sits on the super committee, have repeatedly said that they would fight to roll back the automatic defense cuts, which are known as sequestration, if the panel fails. Those cuts would come on top of spending caps imposed by the debt ceiling law enacted in August, which also established the super committee.

An exact figure for the cuts has been unclear, with the Congressional Budget Office estimating that defense spending is likely to drop by $882 billion over 10 years when factoring in the debt ceiling law and sequestration. However, opponents of defense cuts contend that the overall figure would be about $1 trillion.

“What I have done along with Sen. McCain is that we’re sending a letter to the Pentagon, ‘Please explain to us what would happen to the military if we had a trillion-dollar reduction over the next decade,’” Graham said in a brief interview. “We want to get their view of what would happen to the force if you did $400 billion and then $600 billion.”

McCain and Graham have a long history of working on foreign relations and military issues together, and the Arizona Republican noted that the two are “working together on a proposal” to deal with fighting the defense cuts if the super committee fails.

When asked whether he and Graham were consulting with leadership, McCain said that he and the South Carolina Republican were first working on their offering together before working with leaders.

Leaders signed off on the automatic spending cuts as part of August’s debt ceiling law, making it tough for them to fight a deal they already agreed to.