On Wednesday the President will address the nation on the IS threat and his proposed course of action.

Mr Obama, Vice-President Joe Biden, Secretary of State John Kerry and senior officials were joined at a working dinner at the White House by a coterie of former national security staff from his own administration, as well as one-time advisers to presidents George W. Bush, Bill Clinton and even Jimmy Carter.

The President looked "forward to engaging with this group and hearing their views on a range of national security and foreign policy issues", the White House said.

Just a few hours earlier the White House spokesman Josh Earnest told reporters that Wednesday's speech was not yet written. He could not say whether the speech would be used to more clearly explain to Americans the threat of IS and the existing measures being taken against it, or to announce a new and expanded course of action.

Nor could he say whether or not the President would be calling on Congress to authorise a wider military action against IS, or the expansion of military action into Syria, though that appeared to be implied.

"What the President has said is he - and he said this, again, in the interview that he conducted over the weekend - is his willingness to go wherever is necessary to strike those who are threatening Americans," Mr Earnest said.

Mr Obama told NBC Meet the Press host Chuck Todd on Sunday that the United States will "start going on some offence" against IS: "I just want the American people to understand the nature of the threat and how we're going to deal with it and to have confidence that we'll be able to deal with it."

So far all that seems certain about the speech is that the President will stand by his decision not to return US ground troops to the region in force, as well as an emphasis on the importance of gaining local and regional support for any military action, and NATO and international support for any extension of air strikes.

He has invited the leadership of both parties in Congress to join him at the White House for meetings on Tuesday, though it seems his team has already been building bridges to congressmen.

Asked on Monday afternoon what he wanted to hear from the speech,  Ed Royce, a Republican from California and chairman of the House Foreign Affairs Committee, called for reassurance that allies like Australia were involved.

"So we want to hear a plan, I think, that brings our allies on board, that isn't just the United States doing the air strikes, but other NATO members and other countries like Australia that have indicated a willingness to join with us, other countries in the region providing infantry, and certainly expecting the Kurdish and Iraqi security forces, Free Syrian Army to be armed, and, lastly, no US troops on the ground there, no combat troops," he told CNN on Monday afternoon.

House Intelligence Committee Chairman Mike Rogers  praised Mr Obama, saying his commitment to taking down the group and building an allied coalition marked a "gear shift".

Appearing on MSNBC, the Michigan Republican was asked if he likes what he has been hearing from the President recently regarding IS. "I do. I do," he responded.

Mr Rogers added that he wants the President to target IS militants not just in Iraq, but also in Syria.

The Democratic Senate Intelligence Committee chairwoman, Dianne Feinstein, who has been critical of Mr Obama's handling of the IS threat, told CNN's State of the Union on Sunday that  "I want to congratulate the President. He is now on offence."

The time to act, she later added, is very soon: "Time's a-wasting. We've now said that we're going to go on the offensive. It's time for America to project power and strength."

Even former George W. Bush adviser Karl Rove was praising Mr Obama, saying that "it's a good start, and I have to compliment the President"  on Fox News'  Fox & Friends.