Defense Secretary Ash Carter talks to multinational troops last month in Irbil, Iraq. (Pool/Reuters)

Tim Kaine, a Democrat, represents Virginia in the U.S. Senate.

This weekend marks one year since President Obama initiated U.S. airstrikes against the Islamic State in northern Iraq. In the past year, more than 3,000 members of the U.S. military have served in Operation Inherent Resolve, launching some 4,500 airstrikes, carrying out Special Forces operations and assisting the Iraqi military, the Kurdish pesh merga and Syrians fighting the Islamic State. We have made major gains in northern Iraq and, more recently, northern Syria. But the threat posed by the Islamic State continues to spread in the region and beyond. The war has cost $9.4 million a day, and seven U.S. service members have lost their lives while supporting this mission.

But as the war expands and our troops risk their lives far from home, a tacit agreement to avoid debating this war persists in Washington. The president maintains that he can conduct operations without authorization from Congress. He waited more than six months after the war started to even send Congress a draft authorization for the mission. And recently we’ve heard that the administration may be expanding the scope of the war to defend our trained Syrian fighters against attacks, including from the Assad regime. This could trigger more unforeseen expansions of the ongoing military mission.

Congressional behavior has been even more unusual. Though vested with the sole power to declare war by Article I of the Constitution, Congress has refused to meaningfully debate or vote on the war against the Islamic State. A Congress quick to criticize any executive action by this president has nevertheless encouraged him to carry out an unauthorized war. As far as our allies, the Islamic State or our troops know, Congress is indifferent to what’s happening.

I first introduced a resolution to force Congress to do its job and debate this war in September. That led in December to an affirmative vote by the Senate Foreign Relations Committee to authorize the war, with specific limitations. But the matter was not taken up on the floor because the Senate was about to change to a Republican majority that wanted to analyze the issue afresh. After months of inaction, and to prove that common ground can be found on the contours of this mission, Sen. Jeff Flake (R-Ariz.) and I introduced a bipartisan resolution on June 8 in an attempt to prod the Senate to take its constitutional responsibility seriously. The result? A few discussions in the Senate Foreign Relations Committee, but otherwise silence.

One year of war against the Islamic State has transformed a president who was elected in part because of his early opposition to the Iraq war into an executive war president. It has stretched the 2001 Authorization for Use of Military Force that was passed to defeat the perpetrators of the Sept. 11 attacks far beyond its original meaning or intent. It has shown to all that neither Congress nor the president feel obliged to follow the 1973 War Powers Resolution, which requires that the president cease any unilateral military activity within 90 days unless Congress votes to approve it. And it has demonstrated that Congress would rather hide from its constitutional duty to declare war than have a meaningful debate about whether and how the United States should militarily confront the Islamic State.

The one-year war anniversary coincides with a vigorous congressional effort to challenge U.S. diplomacy regarding the Iranian nuclear agreement. The contrast between congressional indifference to war and its energetic challenge to diplomacy is disturbing.

Last month, I asked Marine Corps Commandant Gen. Joseph F. Dunford Jr., nominated to be the next chairman of the Joint Chiefs of Staff, whether congressional action to finally authorize the war against the Islamic State would be well received by our troops. His answer said it all: “I think what our young men and women need — and it’s really all they need to do what we ask them to do — is a sense that what they’re doing has purpose, has meaning and has the support of the American people.”

One year in, our service members are doing their jobs. But they are still waiting on us to do ours.