It took us President Barack Obama just one TV speech to reverse the supposed central tenets of his presidency on Wednesday night.

He rose to political prominence in part because of early opposition to the Iraq war and he shied away from air strikes on Syria last year.

But now Mr Obama has picked up the war drum and beaten it resoundingly, authorising strikes in Syria for the first time in a military campaign against the Islamic State (Isis) terrorist group.

The president claimed that while there was no evidence Isis was plotting to strike the US, “if left unchecked, these terrorists could pose a growing threat beyond the region, including to the US.”

More US troops will be sent to assist Iraqi security forces and conduct intelligence flights, bringing the total dispatched to more than 1,500.

“We will hunt down terrorists who threaten our country, wherever they are,” Mr Obama said.

“I will not hesitate to take action against Isis in Syria, as well as Iraq.” And he warned: “This is a core principle of my presidency. If you threaten America, you will find no safe haven.”

But the military would not be dragged into a ground war, Mr Obama claimed.

“American forces will not have a combat mission,” he said, and the campaign “will not involve American combat troops fighting on foreign soil.”

US senators seized on the president’s apparent confusion.  “No boots on the ground sounds odd when 1,100 US troops have been sent back to Iraq,” commented Republican senators John McCain and Lindsey Graham, both of whom are members of the Senate armed services committee. 

“Additional US special forces and advisers are needed to direct precision air strikes, advise foreign partners on the ground and possibly conduct targeted operations against the Isis leadership.”

However, not all Senate views were so hawkish.

Democratic senator Mark Udall, also a member of the services committee, said: “The American people must be assured we are not pursuing another open-ended conflict in the Middle East and I will not give this or any other president a blank cheque to begin another land war in Iraq.”