Why were U.S. troops in Niger on Oct. 4, the day four Green Berets were killed in an ambush by a much larger enemy force?

Don't ask Sens. Chuck Schumer, D-N.Y., and Bob Casey, D-Pa. They admitted, or claimed, in interviews over the weekend that they had no idea our forces were even operating in Niger.

Don't ask Sen. Lindsey Graham, R-S.C., either. "I didn't know there was a thousand troops in Niger," said Graham, who sits on the Armed Services Committee and has attempted for years to cultivate his image as a knowledgeable foreign policy hawk. Graham then tried to change the subject by echoing other senators' complaints that Congress is too often kept in the dark about such operations.

But the thing is, Congress wasn't kept in the dark about the operation in Niger, either by the Obama or by the Trump administrations. Far from being a state secret, the information was known not only to several members of Congress who labor in obscurity on Capitol Hill, but also to anyone who has bothered to watch the relevant hearings on C-Span.

"It's not new," Rep. Charlie Dent, R-Pa., told CNN's Chris Cuomo this week. Dent may not get as many appearances on "Meet the Press" as Graham, but the retiring House member from Allentown was well aware of America's presence in Niger when asked. He chairs the House appropriations subcommittee that set aside money to improve runways at U.S. airbases to support the operation in Niger. That appropriation, like all others, had to pass the Senate as well.

"Lawmakers that seem to be aghast at these missions going on are simply not well-read," Dent said. "We have a presence there. Not just there, but within that whole Lake Chad region, supporting local troops to fight Boko Haram, ISIS of West Africa, and of course we're supporting the French operation in Mali. So we do have all sorts of people in that region fighting a very dangerous foe, and ISIS in West Africa, especially."

If Dent can take the time to read up on this operation from his appropriations perch, what excuse is there for Sens. Graham and Schumer (an ex officio member of the Senate Intelligence Committee) for acting as though this is a huge surprise to them?

Sometimes people ask why Congress has allowed the executive branch to usurp its constitutional authority to declare war. Here we have the answer. Members of Congress have become lazy when it comes to military activity abroad because they know that their laziness will be rewarded. Because they don't conduct the necessary study and oversight as a matter of routine, no one holds them accountable when things go wrong.

The fight against terrorists in Niger is, legally speaking, part of the fight against Islamic terrorist groups that was authorized by Congress 16 years ago. But strictly speaking, that authorization only allows operations against those who staged the 9/11 attacks and those who harbored them. That 2001 Authorization for the Use of Military Force, or AUMF, is way out of date, and it's being used to justify many activities that don't fit its terms.

One must wonder whether members of Congress from 2001 (some of whom are still there) would have approved the use of force in such expansive and open-ended terms as they did, if they had been told that future Congresses would be completely ignorant of where the troops were being deployed and what missions they were on.

There could hardly be a better illustration of the need to rescind the 2001 AUMF and replace it with a clearer, limited authorization that updates the threats and perhaps limits how long the authorization lasts without renewal.

Congress has neglected its duty. It must get involved again in the War on Terror. This begins with with a process of members educating themselves on what's being done in their name, not just in Niger, but elsewhere, and then making reasoned, informed judgments about what has been effective and what hasn't, and which parts of the mission should continue or which should be modified or ended.

This is what civilian control of the military looks like. Members of Congress owe the public and those in the Armed Forces a clear statement of their mission that actually matches the facts. It's well past time they provided it.