THERE are three things in life that you should never do ambivalently: get married, buy a house or go to war. Alas, we’re about to do No. 3. Should we?

President Obama clearly took this decision to lead the coalition to degrade and destroy the Islamic State in Iraq and Syria, or ISIS, with deep ambivalence. How could he not? Our staying power is ambiguous, our enemy is barbarous, our regional allies are duplicitous, our European allies are feckless and the Iraqis and Syrians we’re trying to help are fractious. There is not a straight shooter in the bunch.

Other than that, it’s just like D-Day.

Consider Saudi Arabia. It’s going to help train Free Syrian Army soldiers, but, at the same time, is one of the biggest sources of volunteer jihadists in Syria. And, according to a secret 2009 U.S. study signed by then-Secretary of State Hillary Clinton and divulged by WikiLeaks, private “donors in Saudi Arabia constitute the most significant source of funding to Sunni terrorist groups worldwide.”

Turkey allowed foreign jihadists to pass into and out of Syria and has been an important market for oil that ISIS is smuggling out of Iraq for cash. Iran built the E.F.P.’s — explosively formed penetrators — that Iraqi Shiite militias used to help drive America out of Iraq and encouraged Iraq’s Shiite leaders to strip Iraqi Sunnis of as much power and money as possible, which helped create the ISIS Sunni counterrevolt. Syria’s president, Bashar al-Assad, deliberately allowed ISIS to emerge so he could show the world that he was not the only mass murderer in Syria. And Qatar is with us Mondays, Wednesdays and Fridays and against us Tuesdays and Thursdays. Fortunately, it takes the weekends off.