Earlier this month, Sen. Chris Murphy announced he would try to amend the Senate’s $612 billion National Defense Authorization Act with a ban on using ground troops against ISIS, the terrorist Islamic State in Iraq and Syria.

Two days later, the House defeated, 231-196, an amendment to the Senate version of the same bill that would have forced a vote in Congress authorizing any military force against ISIS.

It was defeated by Republicans and some Democrats who supported the Obama administration’s claim that its current action against the terrorists is covered by the authorization given to President Bush in Iraq, authorization Sen. Barak Obama opposed and campaigned against to win the nomination in 2008. President Obama had asked for authority to fight ISIS on a limited basis, but fell back on the previous authorization when Congress failed to take it up.

Confusing, isn’t it?

Sen. Murphy concedes his amendment faces defeat if, in fact, it even receives a vote. He sees a clear designation about what the United States is not willing to do — send ground troops — as a way of showing the nation has learned its lessons from more than a decade of wars in the Middle East.

There is, however, at least one grave lesson Congress hasn’t learned. Either you fight or war or you don’t. Half measures have not worked well.

Declaring war is a serious matter. It gives the president and the generals the authority to conduct such wars without interference, as President Roosevelt and generals like Eisenhower and MacArthur did in World War II.

The words in Article 1 of the Constitution couldn’t be more clear. Congress shall have the power “to declare war.” There’s nothing ambiguous or open to interpretation.

Yet, despite sending Americans into armed conflicts so many times in the past seven decades, the Congress has not declared a war since World War II. The United States has fought major wars in Korea, Vietnam and the Middle East, and had minor conflicts under various designations from Grenada to Somalia, with the death toll for Americans alone more than 110,000 and several times that number injured, many permanently disabled.

There have been many rationalizations for this reluctance to declare war, but it boils down to the unwillingness of Congress to act without clear public — meaning voter — backing. Keeping things murky gives political cover to Congress and leaves blame for failure with the president.

The unwillingness to use war declarations also reflects a hesitancy to allow presidents and the military to assume so much control. Yet, ironically, presidents have used this void to expand military missions.

The precedent was set in 1950 when President Harry Truman sent American troops to lead a United Nations effort to prevent communist North Korea from taking over neighboring South Korea. President Truman sought to back the new international body and its potential as a peacekeeper while being quite aware that the public would be reluctant to go to war again so soon. The “police action,” as it was called, ended in a truce and a divided Korea with 54,000 Americans killed.

President Lyndon Johnson’s Tonkin Gulf Resolution, following a minor attack on an American ship by North Vietnam and a fictionalized second attack, received congressional approval. It misled the nation into widening a limited effort in the next Asian civil conflict, in Vietnam. That time, our country counted 58,000 dead in an undeclared and limited war that lost public support and ended in defeat.

That we were also misled into the second Iraq conflict by a president determined to destroy Saddam Hussein is now even admitted by those who did the misleading but argue they were victims of bad intelligence. At best, that was a case of willful ignorance.

A confused public blurred the invasion of Iraq — which had nothing to do with the attacks of 9/11 — with another undeclared military action in Afghanistan, aimed at al-Qaida, the terrorist organization behind the use of hijacked commercial airlines to attack American targets.

We continue to fight undeclared wars with questionable resources — the Iraq invasion was paid for with borrowed money — and limited public support. When Congress declares war it becomes our war, for good or ill. It unites the country. If Congress does not believe it has the public backing to declare, then perhaps the nation should not be sending troops to fight and die.

Congress should be held to account. It has grown too comfortable with letting presidents take full ownership of conflicts, leaving it free to criticize when the effort does not go well. The framers of the Constitution knew that was no way to go to war or fight one.