Senator Rand Paul, R-Ky., wants Congress to do something it hasn't done since World War II: declare war.

Declare war against the Islamic State, that is.

President Obama is reportedly gearing up to ask Congress to grant him the formal authority to continue using force against the Islamic State in Iraq and Syria. But Obama has already used executive action to engage combat forces in both Iraq and Syria without approval from Congress, and that's a controversial and, some say, unconstitutional, act. One that is instep with Obama's unilateral immigration and healthcare action.

Paul maintains that "war cannot be initiated without Congress," and that "conservatives should be more consistent in their criticism of Obama's use of executive authority," The New York Times reported.

The president's executive decision to wage war against the Islamic State is, according to Paul, overlooked by conservatives who criticize Obama's use of executive authority. Because Congress hasn't been able to come up with a war policy on its own, it has given too much authority to the president.

"Conservatives are mad at him about immigration. And they're mad about him using executive authority on Obamacare," Paul said in an interview Saturday. "But this is another example where he doesn't have much respect for Congress, and some conservatives don't quite get that."

The Obama administration claims it has authority to unilaterally initiate force against the Islamic State under two existing laws passed during George W. Bush's term.

The first being the 2001 authorization for the use of military force passed after the 9/11 attacks, which specifically authorizes force to be used against those responsible for the 9/11 attacks. Obama cited that AUMF when he carried out strikes against suspected terrorists in Yemen and Somalia, according to The New York Times.

The second was a 2002 AUMF issued to President George W. Bush for the Iraq war.

Both are used by the White House as legal justification for fighting the Islamic State without the need for congressional approval. The first 2001 AUMF is relevant, according to the White House, because we are now fighting the Islamic State, which is similar in nature to al-Qaeda. The 2003 AUMF to invade Iraq is applicable because, instead of invading and initiating regime change in Iraq, we are now protecting Iraq.

Paul proposes a repeal of the 2002 AUMF and would like to end the 2001 AUMF after one year, but faces an uphill battle even amongst his own party, who often take the traditional interventionist approach.