WASHINGTON It is often argued, including by me, that the GOP needs its own Bill Clinton or Tony Blair - a leader to reposition the party and reinvigorate its political appeal. But if these figures are examples of successful reform, British Prime Minister David Cameron is a warning of its perils.
Cameron set out to modernize the Conservative Party. He has found that not everyone is happy to be modernized.
The Tory base is tetchy. Some of this is due to a perception that Cameron is insufficiently skeptical of European integration - an issue without exact parallel in American politics. But Cameron's embrace of environmentalism and gay marriage has also caused criticism from older, less cosmopolitan party regulars.
The lesson for the Republican Party is sobering: A political coalition being stretched is at risk of being shattered.
For the GOP - beating against heavy demographic and generational tides - the attempt to modernize is unavoidable. In the next few elections, the ebb might be overcome with just the right presidential candidate, in just the right political circumstance. But in the long run, Republicans are borne away from power. There won't be enough white and gray voters to win national elections.
The fundamentalist approach to reforming the GOP - an oversimplified Reaganism, advocated in the tone of Barry Goldwater - would only hasten the decline. It is an appeal to an electorate increasingly confined to Republican primaries.
But parties generally don't get to reformulate their appeal from scratch. Although Republicans can't win with their base alone, they also can't win without it. Religious conservatives, for example, are the single largest constituency within the GOP, and compose about a quarter of the entire electorate. Such voters are not baggage thrown overboard to lighten the ship; they are planks in the hull.
So the Republican Party is left with a challenge: It needs to become more socially inclusive without becoming socially liberal.
Some of this adjustment concerns policy. The GOP will need to welcome new Americans and champion their economic and social mobility. It will need to remain true to the stable, pro-life convictions of its strongest supporters, while recognizing broad shifts taking place on gay rights among younger Americans, even within the Republican base.
And it will need to speak to the concerns of working-class families who are the real swing voters in national elections. Conservative principles must be applied to new problems, such as stagnant wages, the loss of blue-collar jobs and routine educational failure.
But the Republican readjustment will also require a leader of a certain type. There is one combination that makes this transformation work at a national level: a reform-minded Republican who has the sympathy of religious conservatives.
This would involve an imaginative leadership maneuver. A Republican reformer cannot use religious conservatives as a foil. He or she will need to appeal to religious conviction as a motivation for reform.
A few are trying. Rep. Paul Ryan, R-Wis., invokes Catholic themes when talking about the need to promote economic mobility. Sen. Marco Rubio, R-Fla., has made a persistent religious case for immigration reform.
Few GOP prospects are fighting to occupy this ground. But it is the creative response to the Republican reform dilemma to make religious conviction a source of outreach. And it might accomplish something Cameron has not: making the party's base a participant in the party's modernization.
Michael Gerson's email address is email@example.com.