Prime minister David Cameron’s argument in the Commons for permission to bomb Syria was not based on any new or coherent strategy. As he himself pointed out, it merely follows the logic of a previous vote to bomb Iraq. Even so, like Tony Blair before the Iraq invasion of 2003, he had to rely on abusing his opponents, scaring the public and disseminating dubious intelligence.

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Nothing so undermined the prime minister’s plausibility yesterday as his refusal simply and briskly to withdraw the smear that his opponents were “terrorist sympathisers”. It suggested a man so nervous of his case as to be unable to give any quarter. It also opened him to the counter-smear, that his own relentless deployment of the politics of fear makes him terrorism’s “useful idiot”.

Cameron’s case for dropping bombs on Syria – it hardly constitutes “going to war” – emerges from two previous decisions. The first was the invasion of Iraq and the failure to install stability and democracy in the aftermath. American and British policy at the time contributed directly to the rise of Islamic State, by disbanding the Republican Guard and then humiliating the Sunni population. That guard now supplies Isis with the effective core of its army, the same troops who under Saddam would have kept Isis ruthlessly in check.

The second decision was last year to join a raggle-taggle coalition of the half-willing in bombing Isis targets in northern Iraq. The strongest part of Cameron’s argument was that the Commons overwhelmingly backed that coalition. Now the targets had spread into Syria it made no sense to stop at the border. Britain was already supplying intelligence and drone bombing in Syria; a few more sorties by the RAF to placate our French allies would hardly make much difference.

Yet the objection to those decisions remains with equal force today. Cameron yesterday point-blank refused to accept the logic of what he claims to be doing, which is “defeating Isis”. Britain will bomb Isis in Syria, but will not support the only factor that every military expert agrees can make such bombing effective. That is to be in support of a specific ground offensive over the territory bombed.

The government’s Joint Intelligence Committee claims to have mustered an army of “70,000 moderates … based on detailed analysis updated daily”. The attempt of the deputy chief of the defence staff, General Messenger, to substantiate that army before the Commons defence committee on Tuesday was embarrassing. The phantom army sounds like another “dodgy dossier” from the same people that brought us Iraq’s weapons of mass destruction. Sir John Chilcot might perhaps like to stall his Iraq inquiry to embrace its reprise in Syria.

Speaker after speaker in the Commons yesterday asked how bombing Syria would make Britain’s streets one jot safer. The opposite has to be the case. The thesis is an insult to the intelligence.

Cameron has been captivated, like so many prime ministers before him, by the glamour of the air lobby

The role of airstrikes in modern war has barely advanced since the days of Bomber Harris. Bombs destroy buildings and equipment and kill people. They cannot take or hold territory. They cannot secure victory, let alone peace and prosperity.

Air power can be effective in battlefield support for determined ground troops. This may have been the case in Libya and in aiding the Kurdish cause against Isis in Iraq at present. It may have helped contain Isis from straying into non-Sunni territory round Baghdad. But in general it is pointless if not followed up on the ground. Whatever is “degraded” can always be regraded, as Britain showed after the Blitz.

Cameron has no ground troops in Syria – his own or anyone else’s. He has been captivated, like so many prime ministers before him, by the glamour of the air lobby, for whom ground troops are an embarrassing side issue.

The trouble for Cameron in Syria is that the only ground troops worth the name belong not to the joint intelligence committee’s phantom army but to President Assad, whom Cameron wants to topple. In support of Assad are Iran and Russia, from whom Cameron does everything to distance himself.

In other words, the key component of British strategy lies with three potential allies who are anathema. In the light of this we are surely entitled to ask: just how serious is Cameron in wanting to defeat Isis and remove the “existential” threat to Britain? Cameron emerges not as a terrorist sympathiser, but certainly as a terrorist appeaser.

In the three wars fought this century by British governments against Muslim states – Afghanistan, Iraq and Libya – the goals were to topple incumbents or to eradicate supposed threats to Britain. In each of these cases the resulting wars were disastrous for the countries concerned.

A threat of a terrorist incident is not an existential threat to a state. The relentless “nationalisation” of criminal acts, however motivated and however appalling, does not constitute a cause for war. To do so degrades the language of war and aids the terrorist enemy.

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Cameron, if he really believes the threat to Britain’s “values and way of life” is as serious as he says, owes it to the British people to defend them against it. But where are the marines, the Grenadiers, the Blues and Royals? Where are the billions spent each year on defence? Where is the leadership to deploy this awesome power when the threat is so grave?

In the Commons yesterday Cameron admitted that his strategy is “a long-term objective”. He implied he just wants to be seen helping the Americans and the French. He wants to be seen doing something. His speech was pure mission creep: “Oh well, we are doing what we are doing already, so let’s do a bit more.”

Isis will one day disintegrate, as the Taliban would have disintegrated had they been left alone in 2001. It will disintegrate through attrition on the ground, from local forces fighting it to a standstill. That day will only be postponed by its being cast as the global champion of militant Islam.

The British government’s strategy is both incoherent and inconsistent with the declared threat to the British people. So it does what it always does when it can’t think what to do. It bombs.