DADT SHOULD BE AN EASY LIFT — BUT IT’S NOT…. There’s no shortage of contentious political disputes in Congress right now, but getting rid of the “Don’t Ask, Don’t Tell” policy should be fairly straightforward.

After all, repealing DADT enjoys the support of nearly 80% of the country. A compromise worked out this week enjoys the support of the White House, the Pentagon, and the leadership of both chambers. Joint Chiefs of Staff Chairman Adm. Michael Mullen has endorsed both repeal and the compromise measure, as have two of his predecessors. Even Dick Cheney is on board.

So, this is an easy one, right? Well, it should be, but in this climate, even wildly popular, common-sense proposals can come up short.

Yesterday, a few key senators announced their positions, and not all of the news was good. To her credit, Sen. Susan Collins (R) of Maine said she’ll support DADT repeal, but Sen. Scott Brown (R) of Massachusetts, who was considered a possible pick-up, announced his opposition. Perhaps more alarming, Sen. Jim Webb (D) of Virginia, a member of the Senate Armed Services Committee that will likely vote on this tomorrow, said he’ll oppose repeal.

With some center-right Dems wavering, and Republicans nearly unanimous in their opposition, Roll Call reports this morning that ending the discriminatory policy remains “in doubt” the day before expected votes.

Gay rights advocates and their allies were furiously whipping a deal brokered Monday by the White House that would attach the repeal of the “don’t ask, don’t tell” law to the defense authorization bill. House Democrats face a floor fight on the issue, perhaps later this week, while the Armed Services panel is gearing up for a pivotal vote on the issue Thursday.

Armed Services Chairman Carl Levin said Tuesday he still is not sure whether he has enough support to overturn the policy and will be talking to his colleagues heading into this week’s markup.

Democrats enjoy a 16-12 edge on the committee, but with Webb voting with the GOP on repeal, and no committee Republicans willing to do the right thing, there’s very little margin for error.

In the House, Rep. Patrick Murphy (D) of Pennsylvania is confident he has the votes, but there are still plenty of Blue Dogs who put the measure’s fate in jeopardy. Complicating matters, repeal would be added to a defense appropriations bill, which many liberals Dems intended to vote against since it funds wars they disagree with. The repeal amendment may pass, under one scenario, only to see the larger spending bill falter for different reasons — conservatives will oppose it because it ends discrimination, and liberals may oppose it because it finances current military policies.

Monday’s agreement was a breakthrough, and I’m still cautiously optimistic, but this isn’t going to be easy. Proponents of ending the existing policy are hoping to see the public get more involved in contacting members’ offices over this issue, particularly today. Stay tuned.

Update: Sources tell me Sens. Ben Nelson (D-Neb.) and Robert Byrd (D-W.Va.) will support repeal. This is unconfirmed, but if true, makes success more likely.

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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.