America is at war with the Islamic State, but we are failing to confront the cost of this war.

Deployments of American special operations forces to Syria and Iraq in recent months have rightly revived calls for Congress to pass a new authorization for the use of military force against the Islamic State. A war worth fighting is a war worth debating, authorizing and funding, so Congress should consider the proper scope and strategy of the mission, vote to authorize that strategy, and find a way to pay for the conflict.

There is little precedent in pre-9/11 American history for charging into war without finding a way to pay for it. From the War of 1812, for which Congress approved new taxes in three consecutive years, to the Gulf War, Congress took steps to pay for every major conflict.

Yet, Congress has failed to offset the cost of the post-9/11 wars in Iraq and Afghanistan. The Office of Management and Budget estimated in 2002 that the Iraq war would cost $50 billion to $60 billion. The real cost: $1.64 trillion, plus an additional $715 billion for the war in Afghanistan.

Those totals don’t even incorporate the large and steadily growing costs of long-term care for our injured veterans and military replenishment. A 2013 Harvard study that includes these factors suggests these wars will cost as much as $6 trillion.

As we pursue our goal of “degrading and destroying” the Islamic State, we cannot write another blank check for war. As of Nov. 30, the United States had already spent nearly $5.4 billion since U.S. airstrikes against the Islamic State began in August 2014. That’s $11 million every day.

Paying for the wars we fight is a matter of congressional responsibility and national security. A large national debt weakens our ability to respond to global threats, undermines our fiscal position and limits our diplomatic flexibility. Congress must not disadvantage future generations because we are too timid and irresponsible to make tough choices.

When we pay for our wars with a credit card, and when the pain of war is felt only by our troops and their families, it is far too easy for our nation’s leaders to send soldiers into harm’s way without a national conversation about the merits of our involvement, and far too easy for those conflicts to drag on. A proper national debate of the anti-Islamic State conflict will demand that Congress and the American people better understand the human cost of the war, too.

Paying for war is also morally responsible. Though fewer than 1 percent of Americans served in Iraq and Afghanistan, we should only go to war as a nation. If the Islamic State is a threat that requires a military response, as I believe it is, as Americans we must ask how we can make sure that our servicemen and women on the battlefield have everything they need to defeat the Islamic State.

If we are asking our troops and their families to sacrifice, we all should give something to that effort. One way to offset rising costs while allowing all Americans to contribute is a temporary war surtax that includes an exemption for our troops and their families. In March, I introduced a federal budget amendment that would impose a temporary surtax to pay for our military operations against the Islamic State. When the Senate reconvenes in 2016, I again plan to explore this option.

We should not declare war today only to declare bankruptcy tomorrow. Paying for the wars we fight is our obligation not only to our service members and their families, but to future generations of Americans whose safety and security depend on it.

Chris Coons is a U.S. senator from Delaware, a member of the Senate Foreign Relations Committee, and a Democrat. He wrote this for the Philadelphia Inquirer.