While the Constitution vests in the Congress the power to declare war, American presidents wield great discretion in initiating hostilities. Lyndon B. Johnson dribbled troops into combat in Vietnam in a series of halfway measures that led to disaster. After taking care to build a broad alliance, George H. W. Bush ordered the assault that threw the Iraqi forces out of Kuwait in 1991. His son, George W. Bush, orchestrated the invasions of Afghanistan and Iraq, after gaining the support of Congress. And recently, without involving the Congress, President Donald Trump has shifted the field of battle to economics by declaring a trade war against China.