Capitol Hill is frustrated by President Obama’s incoherent Libya policy. Three months and $800 million into the operation, Congress is making clear it wants an explanation, with some members seeking a hasty end to the operation. But instead of telling President Obama that he can’t keep bombing Libya, Congress should be telling him he can’t keep bombing Libya without a plan.

The Libyan rebels are doing remarkably well politically and militarily. The cities they control have been governed justly and show they are not inclined toward Islamist-style tyranny. The rebels thwarted a major Qaddafi counterattack on Misurata this month, and have made progress on other fronts as well. The arrows on the map are getting gradually closer to Tripoli, and the mood among the rebels is buoyant.

But in Washington, Mr. Obama’s policy is near collapse. House Speaker Boehner warned this week that Congress can cut funds off for the operation—and many on the Hill are inclined to do precisely that.

Congress is understandably upset that President Obama sought a nod from the Arab League and then got “authorization” for the operation from the U.N. Security Council, but never formally consulted Congress. Unfortunately, some Republicans have joined liberals like Dennis Kucinich to call for enforcing the Watergate-era War Powers Resolution, which purports to limit the president’s ability to command the armed forces.

That’s a shame, because conservatives and presidents of both parties have consistently viewed the War Powers Resolution as unconstitutional—which it is. The Framers of the Constitution knew that wars can’t be run by committees. Congress should not compound the fiasco of Obama foreign policy by permanently weakening the presidency. That would only make America less safe.

What Congress can do is insist President Obama come up with a clear objective and concise strategy.

It is absurd to say that U.S. forces are engaged in Libya for purely humanitarian missions. Were this true, we would not be striking Tripoli directly, including repeated strikes on Qaddafi’s headquarters. If the mission is getting rid of Qaddafi—which it ought to be—then let’s get on with it. We should state this obvious goal clearly and augment the rebels’ ability to take Tripoli. We should join the 15 nations that have formally recognized the rebels, allow them to buy arms, coordinate air power with them more closely, and allow them to access frozen Qaddafi funds.

We also have a large incentive to help the rebels succeed after Qaddafi is gone. A real Libyan democracy will be a friend to the U.S. in a dangerous region. A corrupt oil state probably will not.

Mr. Obama needs a plan to help democracy and the rule of law prevail in Libya after the war. Structuring that properly will take congressional action, which is another reason it is unfortunate that the administration has botched this with Capitol Hill. Congress can help President Obama understand this, and seek a coherent Libya policy.

Christian Whiton is a former U.S. State Department senior adviser and is a principal at D.C International Advisory. He is a frequent contributor to Fox News Opinion.