Sen. Bill Nelson (D-FL) is part of a growing list of lawmakers, on both sides of the aisle, that are urging President Obama to order airstrikes on ISIS bases in Syria.

When Congress returns next week, Nelson is planning to introduce a bill to "ensure there's no question that the president has the legal authority he needs to use airstrikes in Syria." 

Legal analysts and lawmakers have long been at odds over what type of military action requires congressional approval -- the debate flared during the 2011 operation in Libya, and amid the threats of military action in Syria last year.

Nelson's planned bill comes a few days after Sen. Dianne Feinstein (D-CA) said the president is being "too cautious" in his response to ISIS.

Nelson joined Gretchen Carlson this afternoon, saying ISIS needs to be "dealt with now" or else the U.S. will have to deal with them later.

"Any group that says they won't stop until the black flag of ISIS flies over the White House, ya know, their intent is pretty clear," said Nelson.

He says the intent of the bill is to clear up any legal "ambiguity" about striking Syria.

Gretchen asked what will happen if the Senate approves Nelson's bill, and then Obama still refuses to act in Syria.

Nelson said the U.S. must still build a coalition to deal with ISIS, but argued that the "head of the snake" lies in Syria.

Watch the interview above.