By Paul Goodman
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The Conservative Party has had five leaders in the last 20 years, and two leadership contests outside the normal electoral cycle (the challenge to Iain Duncan Smith in 2003, and the poll John Major triggered himself in 1995). It hasn't won a general election during that period.
In the previous 20 years it had two leadership contests. It won four of the six elections that took place in those years and governed for about half of them.
I am not an uber-modernising member of the David Cameron fan club. It's not exactly a secret that, for what it's worth, I didn't vote for him in 2005. But the moral of the figures cited above is obvious.
The 1990 challenge to Margaret Thatcher, the most successful Tory leader in peacetime history, injected a poison into the body of the Conservative Parliamentary Party from which it has never fully recovered.
And the dishonourable Parliamentary Party rules whereby a small proportion of MPs is able to force a context, concealed all the while under the cloak of anonymity, is like a weakness in that body.
The consequence of a leadership challenge to Mr Cameron, if unsuccessful, would be to undermine a Conservative-lead Government that has pluses as well as minuses: Michael Gove's school reforms, Mr Duncan Smith's universal credit, Eric Pickles's council tax freeze – and so on.
And as Tim pointed out this morning, if it were successful Mr Cameron has no obvious successor. Such a person would in any event lead with damaged authority, the curse that eventually did for John Major and helped prevent Michael Howard from taking wing.
Parties whose energies are turned inward are doomed. Remember what happened to Labour during the ten years between 1975 and 1983.
Talking of Labour, that party has had three leadership elections in the last 20 years, and one of them took place only because the leader in question, John Smith, died. It has been out of power during that period for about seven years.
The Conservative Party is the only viable vehicle for centre-right politics in Britain. When it stays together and divides its opponents, the centre-right governs the country, as it did for most of the 20th century.
When it doesn't, the centre-left – or the left itself – enjoys the space to take over. I don't want that to be the story of next twenty years as well as the last twenty. And whatever you think of Mr Cameron, a leadership challenge to him would only make such a prospect more likely.
Political parties weakened by poison don't necessarily recover, any more than people do. They can dwindle into nothingness. I suspect that a challenge to Mr Cameron won't happen, but the question should asked none the less: does the party of Disraeli, Salisbury, Churchill and Thatcher really want to end up as the Judean People's Front?