President Obama sent a draft Authorization for the Use of Military Force to Congress on Wednesday afternoon, seeking a vote on the formal legal authorization of a limited military campaign against ISIS. It's a move that's roiling Capitol Hill and leaving many of his co-partisans a bit puzzled. As one aide to a backbench Democrat put it to me, "why is he doing this?"

After all, in an exclusive interview with Vox published earlier this week, Obama observed that "I have the authority as commander-in-chief to send back 200,000 Americans to re-occupy Iraq" if he wants to:

A 2001 resolution passed in the wake of the 9/11 attacks gives the president broad authority if he wants to use it, and this new, more limited resolution the president is asking for doesn't repeal it. That makes the whole thing look pointless to members of congress who don't want to deal with it. But to a president interested in his legacy, the proposed ISIS AUMF is an important step toward re-engaging congress with questions of war and peace — and toward addressing some still-unresolved issues in executive power raised back in 2001.

The Daschle legacy

One key figure here is Denis McDonough, who is unusual for a White House Chief of Staff in that he has a background that is primarily on foreign policy issues, and is unusual for a foreign policy specialist in having spent his formative years on Capitol Hill. When Barack Obama arrived in the Senate in 2005, he was in an unusually favorable position to attract talented congressional staff. Democrats had taken a beating in both the 2002 and 2004 cycles, so lots of people needed jobs. As a promising freshman, he was able to hire Pete Rouse, who just the year before had been chief of staff to Democratic Senate Leader Tom Daschle. McDonough came into Obama's orbit during the 2008 campaign through Rouse, having been Daschle's senior foreign policy aide during 9/11 and the debate over invading Iraq.

This is not a time primarily remembered by the world as an era of legislative sausage-making. But of course things looked different to Daschle and his team.

The former Senate leader recounts in his 2004 book Like No Other Time that he worried the Bush administration's initial draft AUMF in the wake of 9/11 "was a blank check to go anywhere, anytime against anyone the Bush administration or any subsequent administration deemed capable of carrying out an attack." Daschle writes of a "frenetic series of discussions" he carried out with the White House, aimed at crafting "language that gave the President the authority he needed without making that authority unlimited."

Later, discussing Iraq, Daschle focuses less on the specifics of WMD intelligence or regional strategy than on how "our staffs were negotiating quite intensely with the President's people to hammer out some kind of agreement" on AUMF language, and his disappointment that this proved more difficult than the earlier one.

Authority without limits

In practice, however, that hard work put into the 2001 AUMF hasn't panned out McDonough and others who worked in congress to ensure the grant of authority was limited. Both the Bush and Obama administrations have used its legal authority to mount military campaigns not only in Afghanistan but across the border in Pakistan, and then around the world from Yemen to Somalia to Libya.

While Obama has been promiscuous in the range of military targets he's selected, he's also been relatively restrained in terms of the quantity of military force he's willing to apply to any given problem. His successor, except in the very unlikely event of a Rand Paul win, is quite likely to be more hawkish. And Obama's willingness to stretch the meaning of the 2001 AUMF to encompass a wide range of violent Islamist organizations with no real connection to the 9/11 attack creates a legal principle that could underwrite all kinds of things. Obama has no intention of dispatching hundreds of thousands of troops to Nigeria to fight Boko Haram. But under the prevailing legal order he — or more to the point, his successor — could.

Osama bin Laden has been dead for years now. But it seems clear at this point that a range of violent groups with different degrees of practical and ideological cross-linkages will be a feature of the world for quite a long time. Vaguely worded AUMFs, in that context, tilt the balance of power toward executive discretion and away from congressional involvement.

A step back

Obama's proposed ISIS AUMF doesn't alter the problematic 2001 AUMF. But it does take three important steps back from the brink of a forever war scenario.

It establishes the precedent that a new threat, such as ISIS, can and should be addressed with a new AUMF, rather than with more endless references to the 2001 AUMF.

It repeals the 2002 Iraq AUMF, which Bush sought separately from the 2001 resolution, establishing the precedent that these authorizations can and should be rescinded once their original purpose has expired.

In a way that neither of the Bush AUMFs did, it places limits both on the extent of what is authorized (no "enduring offensive ground combat operations") and the time for which it is authorized — with the AUMF automatically expiring after three years.

In a practical sense, of course, Obama's hands remain untied — which is part of why the debate is vexing to Congressional Democrats who'd rather deal with other things.

But in a political sense, it's a proof of concept. The history of executive-congressional relations on national security is dominated by congress alternating between periods of assertion (notably in the wake of Watergate, but also during the Reagan years with regards to Central America, and in the early 1930s) and periods of abdication. Presidents deliberately trying to jolt Congress into limiting executive authority are very rare. But with his term in office coming to an end, Obama wants to do just that — with an eye toward limiting not just his own authority, but his successor's.