But on the constitutional question, members of both parties were nearly unanimous. The power to declare war is one of Congress' most basic functions, even if it has often been asserted only after military operations were already underway.
"Congress must meet its responsibility to decide whether our military should use force," Senate Majority Leader Mitch McConnell (R-Ky.) said in February.
Only that hasn't happened. War authorization proposals have stalled in both the Senate and the House, and proponents are close to abandoning hope that Congress will ever hold a vote.
"I don't think it's dead, but it's certainly on life support," Rep.
Congress has found one reason after another to delay. When the U.S. entered the war last August, a congressional election campaign was underway, so neither party wanted to launch a time-consuming debate. After the election, a new Republican leadership was taking over the Senate — another reason to wait.
Then GOP leaders insisted that Obama take the first step and propose the kind of authorization he wanted. After Obama's draft arrived in February, Republicans dismissed it as too restrictive.
Committees in both houses have held hearings, but the momentum toward holding a full-scale debate and passing an authorization bill has slowly dissipated.
"All of this is really just a ruse to hide the fact that Congress doesn't want to take up a matter that would be politically difficult and, if the war goes badly, could be politically damaging," Schiff said.
The root of the problem is an odd kind of bipartisanship. The issue divides both parties, and that has produced a shared aversion to risky decisions.
Most Republicans support the war against Islamic State and want to give the president broad authority to pursue it. But since the president in question is Obama, many GOP members loathe the idea of endorsing his actions. Most Democrats support the war too, but they're hesitant to commit themselves too deeply. The 2002 vote to authorize President George W. Bush's invasion of Iraq remains fresh in their memories as a terrible mistake that hurt many of them politically.
So while Congress' paralysis might appear at first glance a simple problem of partisan divide — most Republicans want to give the president free rein, most Democrats want to restrict him — the true picture is more complicated and more subtle.
"This would be easier to do if one party were strongly on one side and the other lined up on the opposite side," Schiff said. "But it divides both parties, and so neither sees a real political advantage in it."
To that dispiriting picture, add one more element: Obama has told Congress that he doesn't need its formal approval to continue the war. The president insists that he has ample legal justification under the 2001 resolution that authorized the invasion of Afghanistan. Many legal scholars consider that a stretch; the 2001 document was aimed at Al Qaeda, not Islamic State, which hadn't been founded at the time. But Obama's assertion has been enough to convince some members of Congress that they don't really need to bother with a new authorization.
"When members of Congress feel no compulsion to act on national security grounds, then they are free to play politics," Harvard Law professor Jack Goldsmith wrote recently. And that's exactly what has happened. Republicans have remained free to criticize Obama for using too little force, Democrats to fret that he may be using too much — but neither side has been compelled to take responsibility for the outcome.
This inaction might become more obvious — and more problematic — if the war against Islamic State expands. Offshoots of Islamic State have popped up in more countries, including Libya, Tunisia, Algeria, Yemen and Nigeria — all of which are potential U.S. targets under Obama's interpretation of the law.
"We're asking people to risk their lives in a war without Congress doing its modest job, which is passing a resolution," said Sen.
He's right. The next time a politician from either party complains that Obama or his successor is stretching the bounds of executive power, ask this question: Why didn't Congress meet its constitutional obligation to authorize this new campaign in the endless war on terror?