Among the things lawmakers need to consider are the convoluted relationships among the various parties and the odd bedfellows that have resulted. For example, this week's airstrikes in Syria targeted the Islamic State and the Khorasan group, another terrorist network that U.S. officials say is a direct threat to the U.S. and Europe. Both are foes of Syrian President Bashar Assad, whom the U.S. wants to see deposed, but the U.S. airstrikes paradoxically may have the unintended consequences of helping him stay in power. Similarly, by helping Iraq's Shiite-led army resist ISIS, the U.S. also strengthens Shiite Iran and its Syrian ally Bashar Assad — much to the dismay of America's Sunni allies in Saudi Arabia, the U.A.E. and Jordan.