Trump's attack on Iran draws Republican cheers, Democratic ire

US lawmakers almost instantly reacted on social media to the US President's shock announcement he had ordered an attack on Iran, with Republican hawks celebrating the move and the other side of the aisle voicing sharp disapproval.

"Good. This was the right call," US Senator Lindsey Graham said.

"The regime deserves it. Well done, President @realDonaldTrump. To my fellow citizens: We have the best Air Force in the world."

Republicans have generally urged a hard line on Iran. Most consistently back Israeli military operations in the region and have been vocal critics of Tehran's policies.

Texas congressman Dan Crenshaw urged people to back Trump: Support President Trump. You think these decisions were easy? They weren’t. You think this means WW3? You’re wrong. You think it means American soldiers deploying to Iran? You’re wrong."

"You think it means long term stability in the Middle East and a safer future for Americans? You’re right. Because the regime that wanted ‘Death to the Great Satan’ is at its end."

Democrats have been reticent about Trump's two-month-old diplomatic effort with Iran, quietly backing its goal to deprive Iran of a nuclear weapon capability.

But criticism of a potential attack by Democrats had ramped up in recent days and early condemnation by party members was sharp.

"Trump is acting fully outside of his authority and is once again trampling on the Constitution. This is an illegal and terrifying escalation," Representative Summer Lee said.

"Dropping bombs on Iran brings us closer to war, not peace, and he is putting millions of lives at stake. Congress must immediately pass our War Powers Resolution to rein him in."

"This is insane," Massachusetts Democratic representative Jim McGovern spluttered.

"Trump just bombed Iran without Congressional approval, illegally dragging us into war in the Middle East. Have we not learned our lesson!?!?"

A rare maverick on the Democratic side is Pennsylvania Democratic Senator John Fetterman, among the chamber's biggest backers of Israel.

"As I’ve long maintained, this was the correct move by @POTUS. Iran is the world’s leading sponsor of terrorism and cannot have nuclear capabilities," he said.

"I’m grateful for and salute the finest military in the world."