Rubio says President Trump 'has an obligation to act' in Syria

"Not only does he have a right, he has an obligation to act," Rubio said.

"The president was authorized to conduct this strike. He's not asking for a declaration of war, he's not committing ground troops over an extended period of time. He was dealing with exigent circumstances," the Florida Republican said. "Obviously, if this is going to be a broader, long-term conflict, it is important that he comes to Congress because we need to pay for it."

Just a week ago -- before Tuesday's chemical attack on a northern Syrian town that killed at least 86 civilians -- the White House said the United States must accept the "political reality" of Syrian President Bashar al-Assad's grip on power.

"As long as Assad is there, you are going to have terrorism emanating from Syria, and that's why he needs to go, in addition to the defeat of those terror groups."

Responding to the chemical weapons attack in Idlib province, the United States on Thursday launched 59 tomahawk missiles against the Shayrat Air Base in Homs Province from which the aircraft carrying the chemical weapons is believed to have taken off.

While strongly defending Trump's swift action, Rubio said the administration is still preparing an overall, longer-term strategy on Syria.

Syrian Foreign Minister Walid Moallem firmly denied that his government was responsible fro the chemical attack. He told reporters at a televised press conference in the capital of Damascus on Thursday that “the Syrian Arab Army has never used chemical weapons and will not use chemical weapons against Syrians and even against terrorists.”

Both Syria and Russia have blamed Syrian rebels for the chemical weapons attack and slammed the United States for its airstrikes.

He said the U.S. airstrike will act as a deterrent to the Syrian leader.

"That is an important airfield," Rubio told "GMA." "It will not degrade his entire capability to do some of this, especially as the Russians continue to support him. But he is certainly not just less capable but, I believe, less willing this morning to do that sort of activity because his cost-benefit analysis just changed dramatically."

ABC News' Conor Finnegan, Benjamin Gittleson, Adam Kelsey, Luis Martinez and Kirit Radia contributed to this report.