Abbott again ruled out combat troops on the ground, saying the 200 Special Forces members being deployed as military advisers to the Iraqi Army and Kurdish Peshmerga fighters would "normally" be based at battalion headquarters. Yet the Pentagon said on Tuesday that US military advisers might accompany Iraqi troops on attacks against Isis targets.
Explaining the decision to join the US mission, Abbott has cited as a material factor the presence of "Australians there in significant numbers who wish to do us harm". The security agencies are clearly on high alert for any links between jihadis in the Middle East and supporters in Australia, as shown by yesterday's dramatic terrorism raids in Sydney.
But the fact that a handful of Australian jihadis have travelled to Iraq and Syria to fight with Isis does not automatically mean they pose a threat at home. The motives driving them to join Isis' murderous ranks would not necessarily impel them to carry out terrorist attacks in Australia on their return.
If Isis is nursing ambitions to extend its caliphate to Sydney and Wagga Wagga, or, indeed, London or Seattle, that's not yet apparent.
A Homeland Security spokesman told a US Senate hearing last week that there was no evidence to support the belief that Isis was planning an attack on US soil.
That's not to argue that they are not a scarily brutal and well-resourced outfit, which, unchecked, could wreak slaughter and mayhem across the Middle East. The question is what threat they pose outside the region.
What's almost certain is that Australia's dash to fight them on the other side of the world will increase its vulnerability as a target. The terrorism alert level was raised to high last Friday, even before Abbott announced the involvement of the Special Forces, together with 400 Air Force personnel and combat aircraft.
The other question is how far Western powers, including Australia, are prepared to go in an effort to "degrade" Isis, given that realists agree they can't be wiped out. Abbott has warned Australians to prepare for a campaign that could last "many, many months". Make that years.
In fairness to Abbott, in his rush to please teacher he is emulating not only John Howard, who stood beside President George W. Bush on 9/11 as the latter announced a "war on terror", but of almost every Australian prime minister since Federation.
The only difference is that teacher used to be Britain. Now it's the US.