U.S. President Barack Obama delivers a statement on legislation he sent to Congress to authorize the use of military force (AUMF) against the Islamic State with U.S. Vice President Joseph "Joe" Biden, left, Washington, D.C., U.S., on Wednesday, Feb. 11, 2015. (Andrew Harrer/Bloomberg)

It may be the triumph of hope over headlines to imagine that a Congress currently incapable of funding the Department of Homeland Security could pass a new war authorization.

Funding DHS should be a no-brainer. Crafting an authorization for the use of military force is fraught with bipartisan disagreements over scope and further complicated by Republican distrust of President Obama.

But the coming crackup over DHS will damage only the Republicans who painted themselves into this legislative corner — and you know how this movie ends. (Spoiler alert: They surrender.) By contrast, failure to approve a war authorization would represent an abdication of constitutional responsibility, with implications far beyond the current Congress.

Granted, it’s odd to be debating whether the president should be authorized to use military force against the Islamic State months after he began doing just that.

Obama’s strained legal position has been that congressional approval would be “welcome” but that he retains the authority to conduct military operations against the Islamic State under the 2001 Authorization for Use of Military Force; it empowers the commander in chief to act “against those nations, organizations, or persons he determines planned, authorized, committed, or aided the terrorist attacks that occurred on September 11, 2001.”

To rephrase Donald Rumsfeld, you go to war with the AUMF you have, I suppose, but this one — written nearly 14 years ago with a different organization and different country in mind — is an awfully shaky justification.

So credit to Obama for coming forward with a more plausible alternative. (He held back earlier, as the Senate Foreign Relations Committee took up the issue during the lame-duck session, on the theory that presidential quacking was not apt to win Republican votes. The committee voted along party lines anyway.)

I am not arguing in favor of the administration’s draft. The ordinary temptation is to figure that the president must be doing something right if both sides complain. Actually, I think critics on the left and right have legitimate points.

Liberal Democrats’ concern is that it gives this president, and his successor, too much power over what force to use and against what groups. Their strongest point is the odd fact that the president has chosen to leave in effect the 2001 AUMF, even though Obama himself has said since 2013 that it is time to “refine, and ultimately repeal” its authority.

If the administration doesn’t believe Congress is capable of writing one authorization at the same time it rewrites another (okay, hard to argue with that), it must at least make clear that the new Islamic State legislation supplants whatever shreds of authority exist under the 2001 document for that purpose.

The Republican criticism is that the president’s proposal would cede too much authority. Yes, that’s right: The president they have assailed as a unilateral executive orderer is not trying to be dictatorial enough.

But once you stop chuckling over the inconsistency, you have to consider — there’s a real issue here. Obama’s suggested restraint on his own authority is both substantive and temporal. He would limit presidential power to commit ground troops and set a three-year expiration date.

I’m not worried about the first. The point of an authorization is not to serve as a presidential blank check. And the administration’s wording — the military is not to be used in “enduring offensive combat operations” — contains more than enough flexibility. (See Democratic distress, above.)

But the expiration date should be removed. What happens when the time expires, hostilities are continuing, and a future Congress is unable to get its act together to reauthorize? (See DHS funding, above.)

An authorization that forswears ground forces is not going to embolden an Islamic State already aware of those limits. A three-year timetable sends a more alarming message: Hang on and the infidels will retreat.

Harvard law professor Jack Goldsmith, who served in the George W. Bush Justice Department, contends that the risk is overblown, writing that “it should not be hard for the next president to make the case . . . if such authorizations are plausibly warranted.” (Really? See DHS funding, above.) Since an 1819 authorization to use force against pirates, there have been only two resolutions with time limits, Lebanon in 1983 and Somalia in 1993.

I’m not so naive as to think passing an authorization will be easy. I’m not so cynical as to believe it’s impossible. Not yet, anyway.

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