THE ONGOING SPLIT BETWEEN GOP AND MILITARY LEADERS…. It wasn’t too long ago that there were certain expectations about political and military policy. If, in the midst of two wars, the Pentagon asked Congress for some help, lawmakers were likely to oblige. This was especially true of Republicans, who took pride in characterizing themselves as the “pro-military” party.

This week, we received yet another reminder that these partisan assumptions are in need of revision.

An unusual split has opened between conservative Republicans and the American military leadership over the U.S.-Russia nuclear treaty, with current and former generals urging swift passage but politicians expressing far more skepticism.

Adm. Mike Mullen, chairman of the Joint Chiefs of Staff, has called the New Strategic Arms Reduction Treaty (New START) “essential to our future security.” Retired generals have been so concerned about getting it ratified that some have traveled around the country promoting it.

Seven of eight former commanders of U.S. nuclear forces have urged the Senate to approve the treaty.

But five Republicans on the Senate Foreign Relations Committee said in a recent report that New START was “a bad deal.” They added that U.S. military leaders had made assumptions about the pact — including that Russia will honor it — that are “optimistic in the extreme.”

Meanwhile, the conservative Heritage Foundation’s grass-roots lobbying arm is targeting Republican senators with mailings warning that the treaty “benefits Russia’s interests, not ours.”

Retired Lt. Gen. Dirk Jameson, the former deputy commander of U.S. nuclear forces, told the Washington Post that it’s “puzzling” that the advice military leaders are giving Republicans is being “ignored.” Jameson added, “I don’t know what that says about the trust that people have and the confidence they have in our military.”

Democrats, I suspect, aren’t willing to make the case in these terms, but that’s why it’s all the more important when someone like Jameson is making these arguments publicly. He’s effectively arguing that most Senate Republicans are blowing off the judgment of America’s military leadership — a charge that used to be unthinkable.

But what’s especially noteworthy here is the consistency in which we’ve seen this pattern. On New START, obviously, the chairman of the Joint Chiefs and the Secretary of Defense are actively urging Senate ratification, but the GOP is convinced they’re mistaken. Mullen, Gates, and other military leaders also want to see Republicans end their filibuster of the National Defense Authorization Act, but the GOP is ignoring this request, too.

In fact, the U.S. military leadership and congressional Republicans are also on opposite sides of everything from civilian trials for terrorist suspects to closing the facility at Guantanamo Bay to Iran to torture to how the U.S. perceives the Middle East peace process in the context of our national security interests. GOP lawmakers haven’t even fared well on some veterans’ groups congressional scorecards.

The notion of Republicans siding with the military is supposed to be one of those assumed truths that we’re all supposed to just accept. But over the last two years, on most of the major policy disputes related to national security and defense, it’s been Democrats (on both ends of Pennsylvania Avenue), not Republicans, who’ve been siding with U.S. military leaders.

Those old partisan assumptions just don’t apply anymore.

Steve Benen

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.