Potential 2016 presidential candidate Sen. Rand Paul is proposing a "declaration of war" against the Islamic State.
The legislative effort has little chance of success but could burnish the Republican's effort to paint himself as a strict constitutionalist as he explores a White House bid. Other lawmakers have proposed authorising military force against Islamic State extremists.
Paul is the first to seek a formal declaration of war. His bill would authorise the president to use the military against the group and its affiliates for one year to protect US citizens and facilities in Iraq and Syria.
Ground combat forces could only be used to shield Americans from imminent danger and to gather intelligence or pursue high-level targets.
Although Congress hasn't formally declared "war" since World War II, presidents have deployed troops without a declaration. President Barack Obama has sent about 3,000 US troops to train and assist Iraqi security forces.
The US-led coalition has launched hundreds of airstrikes against targets in Iraq and Syria since September.
