PENTAGON BUDGET CUTS HAVE TO BE ON THE TABLE, CONT’D…. I continue to believe in a simple litmus test — if you claim to believe in fiscal responsibility and want to cut the deficit, you can’t insist that the Pentagon budget is untouchable. It’s an immediate credibility killer, reflecting a fundamental lack of seriousness about the subject.

On the right, there are some disagreements on the subject. Sen.-elect Marco Rubio (R-Fla.), for example, has said the defense budget is off the table. Sarah Palin and Bill Kristol have said the same thing.

But one of the interesting trends to watch over the next year is the extent to which Republicans are divided on this point. Indiana Gov. Mitch Daniels (R), for example, took a reasonable line yesterday.

Daniels said cuts to defense spending should be on the table: “We need to take a really hard look at the missions we’ve undertaken.”

Sen. Tom Coburn (R-Okla.), one of the chamber’s most far-right members, is thinking along the same lines.

Republicans also should resist pressure to take all defense spending cuts off the table…. Our nation’s military leaders understand the need to cut spending.

As Adm. Mike Mullen, chairman of the Joint Chiefs of Staff, said, “Our national debt is our biggest national security threat.” History shows that every nation eventually adopts the foreign policy it can afford. Taking defense spending off the table is indefensible. We need to protect our nation, not the Pentagon’s sacred cows.

The right really isn’t united on this one, and that’s a good thing. A lot of Tea Partiers have endorsed Pentagon cuts, and we’ve heard some encouraging rhetoric in recent weeks from Illinois’ Mark Kirk (R), Georgia’s Johnny Isakson (R), and Kentucky’s Rand Paul (R). Even Rep. Paul Ryan (R-Wis.), the ranking member on the House Budget Committee, conceded recently, “The Pentagon’s budget itself is not working right, so there are billions of dollars of waste you can get out of the Pentagon, lots of procurement waste. We’re buying some weapons systems I would argue you don’t need anymore.”

Zaid Jilani noted earlier that Pennsylvania’s Pat Toomey (R) and Tennessee’s Bob Corker (R) are also prepared to make cuts to the defense budget.

What’s more, a Sustainable Defense Task Force, led by Reps. Barney Frank (D-Mass.) and Ron Paul (R-Texas), but featuring 55 other lawmakers from both parties, recently sent a letter to the National Commission on Fiscal Responsibility and Reform, recommending sensible, responsible cuts to the Pentagon budget.

This shouldn’t even be controversial. Defense spending will top $700 billion in the next fiscal year. For so many Republicans to insist that we cut spending, but deliberately ignore the largest discretionary portion of the budget, is absurd.

The United States now spends about as much on defense as every other country on the planet combined. Defense Secretary Robert Gates has said, publicly and repeatedly, that the United States can’t keep spending such vast amounts of money on the military indefinitely. It’s simply unsustainable.

It’s the first hurdle that has to be cleared for the rest of the fiscal discussion to even get underway. Those who claim credibility on the subject, but believe a bloated Pentagon budget is untouchable, shouldn’t even be part of the conversation.

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Follow Steve on Twitter @stevebenen. Steve Benen is a producer at MSNBC's The Rachel Maddow Show. He was the principal contributor to the Washington Monthly's Political Animal blog from August 2008 until January 2012.