In his Mail on Sunday column, Vince Cable  reminds us of a Lib Dem policy that deserves to be better known than it is. He writes:
Nor is it honest to say that some government budgets, such as that of the NHS, should be "ring-fenced" from cuts. By doing so, the government and the Tories are condemning other valued services to deeply damaging cuts.
Alone among the three main parties, the Lib Dems have avoided promising to ring-fence spending in any area. It's one stance, along with the party's pledge to raise the income-tax threshold to £10,000, that deserves serious attention.
Could it turn out to be a canny move? The line that all government departments should share the pain equally could prove to be effective. It certainly gives the Lib Dems a chance to split the Tories.
There is growing anger on the Conservative right over David Cameron's pledge to protect the health and overseas aid budgets, while cutting spending elsewhere by up to 20 per cent. The implications for defence, in particular, trouble the Tory grass roots.
This week's Spectator leader (not available online) gives us a flavour of the anger:
As Mr Cameron says, we're all in this together. So why should the police and military suffer, while the NHS bureaucracy keeps every penny of the money it has been force-fed?
The Tory leader's promise to protect spending on the NHS and international development is an essential part of his "detoxification" strategy, but it will cause him immense problems if the Tories win power. With an eye to these tensions, Labour is set to promise  to ring-fence the defence budget for 2010-2011, with a £1.5bn spending boost for the Afghan war.
Cameron's response will be worth studying.