THE DREAM ACT’S BEST SHOT…. This afternoon, when the Senate moves to consider the defense authorization bill, it will mark a key turning point in the debate over “Don’t Ask, Don’t Tell.” But it will also offer an opportunity to pass the Dream Act.

Obviously, Congress lacked the time to tackle a comprehensive immigration reform bill this year, a task that was made more difficult by Republicans rejecting their own ideas. But lawmakers can still make considerable progress on immigration policy by passing the Dream Act amendment to the military spending bill.

The Senate will consider Tuesday whether hundreds of thousands of immigrants who were brought to the United States illegally as children should be placed on a path to citizenship.

The controversial measure is being pushed by Senate Majority Leader Harry M. Reid (D-Nev.), who bypassed usual Senate procedures by including it in a defense reauthorization bill.

Opponents consider the Dream Act a form of amnesty and have accused Reid and other Democrats of using it to appeal to Hispanic voters, an important constituency, as the midterm elections approach. Supporters, who include retired Gen. Colin L. Powell and other military officials, have argued that the measure is long overdue, humane and practical.

If politics made sense, the Dream Act (Development, Relief and Education for Alien Minors Act) would pass easily. It’s sponsored by Majority Whip Dick Durbin (D-Ill.) and Sen. Dick Lugar (R-Ind.) — i.e., it enjoys bipartisan support — and is years in the making.

Every year, tens of thousands of young illegal immigrants graduate from American high schools, but are quickly stuck — they can’t qualify for college aid, and they can’t work legally. America is the only home they’ve ever known — in most cases, they were brought into the country illegally by their parents — but at 18, they have few options.

The DREAM Act provides a path to citizenship for these young immigrants — graduate from high school, get conditional permanent residency status, go to college or serve in the military, and become eligible for citizenship.

The measure will, of course, need 60 votes. In theory, that shouldn’t be difficult. Not only is Lugar co-sponsoring the bill, but Sen. Orrin Hatch (R-Utah) helped write the policy a few years ago. Better yet, Sen. John McCain (R-Ariz.), before his transformation into a right-wing hack, has not only supported the Dream Act for years, he even promised the National Council of La Raza two years ago that he would support the bill if elected president.

Now, however, as the GOP has moved even further to the hard-right, supporters of the Dream Act have become opponents. Hatch and McCain, for example, have done 180-degree turns without explanation. Some so-called “moderates” have decided to toe the right-wing line — Sen. Scott Brown (R-Mass.) has condemned the proposal as “amnesty” for illegal immigrants, despite the fact that it’s not these kids’ fault that they’re undocumented. Some center-right Dems may balk at the policy, too.

Unlike DADT repeal, the Dream Act is not already in the defense bill, but teh Senate leadership hopes to add it as an amendment. It’ll need 60 votes, but the odds aren’t good.

If it fails, progress will likely be pushed off indefinitely, after expected Republican gains in the midterms.

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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.