The US Constitution granted separate war powers to both Congress and the President, and neither branch has refrained [PDF] from exercising those powers. During the 19th century, Congress formally declared three wars and authorized the president to engage in military actions on several occasions. In July 1798, President John Adams received approval from Congress to enter the Quasi-War with France and capture French warships. In February 1802, Congress authorized Thomas Jefferson to use military force against Tripoli in the Barbary War. Congress formally declared war for the first time against Great Britain in June 1812. The next formal declaration of war occurred in May 1846, when Congress declared war on Mexico. Congress declared war once more during the 19th century, against Spain in April 1898.
The 20th century saw the formal declaration of war fall to the wayside. The US entered World War I in 1917 after Congress formally declared war against Germany that April, and then against Austria-Hungary that December. World War II was the last war formally declared by Congress, with declarations issued against Japan on December 8, 1941, Germany and Italy on December 11, 1941 and Bulgaria, Romania and Hungary in June 1942. President Franklin Roosevelt interned American citizens of Japanese descent during World War II, and the US Supreme Court held the internment lawful in 1944. In June 1950, the US entered the Korean War upon the orders of President Harry Truman. Truman attempted to use his emergency powers in 1952 to seize production of steel facilities, but the Supreme Court held that the seizure was unconstitutional.
The Vietnam War marked a turning point for the President's war powers.
In August 1964, Congress passed the Gulf of Tonkin Resolution and authorized President Lyndon Johnson to take military action in Southeast Asia. In response to concerns about war powers and the unpopular Vietnam War, Congress legislated the War Powers Resolution in 1971 to regulate executive war powers.
The passage of the War Powers Resolution did not prevent presidents from exercising their war powers. President Gerald Ford evacuated American personnel from Vietnam in April 1975. Jimmy Carter attempted to rescue Americans using US personnel during the Iran Hostage crisis in 1980. Ronald Reagan launched the 1983 invasion of Grenada. George Bush Sr. received approval from Congress to launch the First Gulf War in 1991. William Clinton oversaw several military actions, such as deploying warships to enforce an embargo against Haiti in 1993.
Following the 9/11 terrorist attacks, President George W. Bush launched the invasion of Afghanistan in October 2001. Bush later commenced the invasion of Iraq, the Second Gulf War, in March 2003. The presidential use of military force abroad has continued into the administration of President Barack Obama. In March 2011, Obama lent US air support to operations in Libya and that May ordered the attack that killed Osama bin Laden. In August and September 2013 President Obama contemplated overt military action to intervene in the ongoing Syrian conflict. The question of congressional war power approval surfaced once again. Senator Obama was a critic of presidential use of War Powers Act when the military action was not to stop an imminent or direct threat to the United States. Overt military action in Syria never came to fruition and the debate over the War Powers Act persists.