Washington: It was quite weird. When the Washington talking heads assembled on Sunday morning for their weekly agenda-setting TV talk show jamboree, the question hardly asked and barely answered was how real or credible was the security threat posed by the so-called Islamic State to the West?

Outlining his case for war last Wednesday, President Barack Obama was obliged to concede the US "[had] not yet detected specific plotting against our homeland".

But that didn't stop the Bobbsey Twins of US politics, Republican senators, Lindsey Graham of South Carolina and John McCain of Arizona.

Graham was demanding Obama dispatch US troops back to Iraq "before we all get killed here at home". McCain, too, was adamant Obama was not doing enough: "That is simply a very narrow and focused approach to a problem which is metastasizing as we speak. … [IS] is attracting extreme elements from all over the world, much less the Arab world. And what have we done?"

Figures become inflated or conflated to suit the argument de jour; McCain was throwing around the number 100. McCain insisted this was the number of Americans fighting with IS but, in correcting him, terrorism expert Peter Bergen said it was the total number of Americans believed to have fought or attempted to have fought with any of many Syrian insurgent groups in the course of the conflict, some of which, even in Washington's book, are deemed to be good-ish guys.

In testing Obama's "no specific plot" line with White House chief of staff Denis McDonough, CBS's Face the Nation host Bob Schieffer extracted this response: "What we have said is that we are not aware of any credible threats to the homeland right now.

"But we are concerned about three things in particular. The fact that they now control territory and that gives them place to plot and plan. The fact that they are now getting not only new fighters but increased money and followers and adherents. Third, and perhaps most importantly, we're worried about the number of foreign fighters that are going into Syria to fight.

"Some of them may then become even more extreme and want to return to their home countries, be that in Europe or even in the United States, God forbid, to carry out their terrible acts."

But when that "third and perhaps most important" point is tested in the context of Washington's leadership of the emerging coalition to "degrade and destroy" IS, it doesn't hold a lot of water.

Again it was Bergen who was something of a spoilsport, pulling out figures on the last time people living in the US signed on for holy war. It was in Somalia in 2006, when Washington backed an invasion by Ethiopian forces and more than 40 Americans signed on with the al-Qaeda affiliate al-Shabbab.

Just as is the case today in Syria, for a good number of the Americans who went to fight in Somalia it was a one-way ticket because 15 of the 40 or so US volunteers died there either as suicide attackers or on the battlefield.

Then, as now, there were apocalyptic warnings.

This on the Americans in Somalia from Republican congressman Peter King, then chairman of the House Homeland Security Committee, in 2011: "With a large group of Muslim-Americans willing to die as 'martyrs' and a strong operational partnership with al-Qaeda leaders in Pakistan and in Yemen, al-Shabbab now has more capability than ever to strike the US homeland."

None of them is known to have returned to the US, as sleeper cells or lone wolves, to attempt a terrorist attack. But never mind, here's King on NBC a few weeks back: "[IS] is a direct threat to the United States of America ... They are more powerful now than al-Qaeda was on 9/11."

With the Syrian conflict in its fourth year and Iraq in the whiplash of war for more than a decade, it's hardly surprising there has been a handful of charges against individuals for supporting the extremist groups. However, none of the returned jihadis has been charged with plotting terror in the US.

In the same vein, al-Qaeda in Iraq, the movement from which IS sprung, bombed three US hotels in Jordan, but is not known to have mounted an attack inside the US.

Bergen and his co-author David Sterman acknowledge that with more than 1000 European passport-holders, British and continental security services may face a greater risk in returning fighters bringing the war home with them, and many may enjoy visa-free access to the US.

But they write: "It's worth noting that, in none of the successful terrorist attacks in the [US] since 9/11, such as the Boston Marathon bombings last year or Major Nidal Hasan's massacre at Fort Hood, Texas, in 2009, did any of the convicted or alleged perpetrators receive training overseas."

Paul Pillar, a former deputy director of the CIA's Counterterrorism Centre, worries there has been a complete misreading of IS, especially in the parallels with al-Qaeda.

"The American public has come to equate advances in the Middle East by this one group …with the danger of another 9/11," he told The Washington Post. By his reckoning, IS tactically can be seen as the opposite of the Osama bin Laden organisation and that, in making it the target of a US-led campaign, Washington risks turning its focus toward the US, and ditto Canberra.

"For them to seize and maintain territory is a major digression from terrorist operations in the West, rather than a facilitation of such operations," he said. US strikes could degrade IS, but he added: "There will be a revenge factor. The killing of the two captive [US] journalists was depicted by the group explicitly as retaliation for strikes that had already occurred."

But while the White House acknowledges the possibility of revenge attacks, officials are marking IS down as a different terrorist breed from the al-Qaeda spin-offs that have attempted to strike at US targets. IS is not yet believed to have the professionalism or patience to work up international plots or intrigues.

"[IS]'s ability to carry out complex, large-scale attacks in the West is currently limited," Nicholas Rasmussen, deputy director of the National Counterterrorism Centre, told a Senate committee last week. By contrast, he said, the Yemen-based al-Qaeda in the Arabian Peninsula "remains the al-Qaeda affiliate most likely to attempt transnational attacks against the United States".

Daniel Benjamin, a former counterterrorism co-ordinator for the US State Department, was one of the few TV talking heads who attempted to hose down rampant public expectations of terrorist attacks in the US, which the political classes are doing little to quell because the midterm congressional elections are just weeks away.

"I do think the threat has been exaggerated a bit domestically," Benjamin said on ABC's Sunday talk show. His argument was that, since the September 11 attacks, the US had spent hugely to bolster its systems for detecting the threat posed by terrorists entering the country.

"We have a bad history of thinking it's all about us," he said, "as we did in Vietnam, as we did in thinking that Saddam Hussein was going to be a threat to us when he was trying to keep his own people cowed and subservient."