 -- The question of whether President Donald Trump needs congressional approval for military airstrikes has been raised following Thursday's U.S. launch of 59 missiles against an air base in Syria.

The answer depends on which expert or lawmaker you ask.

By and large, it is understood that a president can respond militarily to a crisis -- at first, in a limited way -- without approval from the legislative branch. Still, some scholars, and plenty of lawmakers, believe that only applies if the U.S. itself is attacked.

Thursday evening, several lawmakers said they did not think President Trump needed approval for this type of limited military action.

"Unlike the previous administration, President Trump confronted a pivotal moment in Syria and took action," said Sens. John McCain, R-Ariz. and Lindsey Graham, R-S.C. in a joint statement. "For that, he deserves the support of the American people."

Still, most lawmakers believe that any continued involvement in Syria would need to be legally justified either under the current 2001 Authorization for the Military Force or a new AUMF from Congress. The 2001 AUMF passed in both houses after the attacks on September 11, 2001 and gave the go-ahead for military involvement in Afghanistan.

The language of the 2001 AUMF authorized "force against those nations, organizations, or persons" that "planned, authorized, committed, or aided the terrorist attacks that occurred on September 11, 2001, or harbored such organizations or persons."

An AUMF is typically used for a protracted military campaign. For years, some lawmakers and even military officials have argued that the 2001 AUMF is outdated and could not or should not be stretched to cover any further campaigns.

Voting on a new AUMF could be a hard political sell. In 2011, President Obama did not receive a new AUMF for military action against Libya.

Thursday night, some lawmakers called for the House to come back into session to debate the merits of a new AUMF.

"This missile strike and the military action of our forces already in Syria, have yet to be authorized by Congress," said Rep. Adam Schiff, D-Calif, the ranking member on the House Intelligence Committee. "I will be re-introducing an authorization for use of military force against ISIS and al-Qaeda when Congress returns to session. Congress cannot abdicate its responsibility any longer and should vote on any use of force not made in self defense."

Others in the senate questioned whether the Trump administration had acted within its authority.

"While we all condemn the atrocities in Syria, the United States was not attacked," said Sen. Rand Paul, R-Ky. "The President needs Congressional authorization for military action as required by the Constitution, and I call on him to come to Congress for a proper debate."

Sen. Tim Kaine, D-Va., said he would "work with the President, but his failure to seek Congressional approval is unlawful."

Talks are ongoing in the senate about the possibility of a new AUMF. In 2013, Obama punted on acting unilaterally and asked Congress to approve any military action in Syria. With both parties divided, it did not pass.

At the time, Trump tweeted that Obama's move to ask for congressional approval was necessary.