President Trump should have sought a vote on authorizing military force in Syria before ordering Thursday's cruise missile strike, Sen. Tim Kaine said Friday.

Kaine, speaking on CNN, said Trump did the right thing on moral grounds, but there's no legal justification for the strike on an air base in central Syria.

"He should not have done this without coming to Congress," Kaine said.

The strikes took place around 8:40 p.m. Eastern time Thursday night and were only confirmed following the attack. While some members of Congress were notified of the strikes, the majority found out through press reports, Kaine said.

That's unacceptable under the Constitution, the Virginia Democrat said.

"He did this unannounced," he said. "The Constitution is very clear. Whatever you think of Congress, the Constitution is very clear: Congress declares war."

When pressed by CNN anchor Chris Cuomo about Congress' reluctance in recent decades to get more involved in declarations of war — Congress hasn't issued a formal declaration of war since 1942 — Kaine said the legislative body must take back its constitutional powers.

"It's time for us to get in the game," he said.

Kaine, who pushed President Obama to seek congressional authorization for his proposed actions in Syria, added, "There is no authorization that covers this. That means we have to bring it, we have to have the debate … but he took an oath to the Constitution, as we did, and we need to follow through with it."