Today is the Conservatives’ defence day – featuring a commitment by Michael Fallon to renew Trident in full alongside a tasteless attack on Ed Miliband…and a noticeable silence.  The subject of the latter is the commitment which NATO seeks from its members to spend two per cent of GDP on defence.

It seems to be the case that security policy is not coming up much on the doorstep during this election – as an experienced observer of defence politics, himself a passionate supporter of the armed forces, admitted to me recently  George Osborne is right to have anticipated as much, and to believe that a election commitment to meet the NATO target of spending two per cent of GDP on defence would sway few votes towards the Conservatives.

The Government is already committed to increasing the defence equipment budget in real terms. And  in any event, targets aren’t a be-all-and-end-all.  Some of the same people who claim in one breath that a target for aid spending is inherently absurd assert in the next the inviolable sanctity of the NATO target.  Nor is all defence spending effective spending (consider the long tale of the Eurofighter).  Procurement is legendary for waste, although the Fox/Hammond reforms at the department have certainly improved its performance.

There is thus a case for arguing that the senior military – some of whom are no slouches at running forceful public campaigns for bigger budgets – must prepare for the coming Strategic Defence Security Review without a commitment to the two per cent target.

The reason why it isn’t persuasive is horribly simple, and can be summed up in a single word: Russia (or Putin, if you prefer).  There is little that we can do for Ukraine – or arguably should, given both the limits of our military obligations and the story of how it reached its present pass, in which the EU is far from blameless.  The Baltic States are a different matter.  As a NATO member, we are committed to defending them.  Putin may have no plan whatsoever to absorb them into Russia.  But it would be unwise to take a chance on it – and, by not meeting the NATO target, risk flashing him a green light.

Then there is the number one threat to our own internal security to consider: violent Islamism.  Preparing for the worst requires military as well as police preparations.  A commitment to meet the target is necessary when the Conservative Manifesto is launched next week.  It might not make an impression on voters, but it certainly would on Tory backbenchers.  Their support will be badly needed after May 7 if David Cameron returns to Downing Street.  And in any event, it would be the right thing to do.

Bashing Miliband over Trident is necessary. But not sufficient.