"Pray take away this pudding," Winston Churchill commanded one night at dinner. "It has no theme." Our two political parties, facing the first election in 80 years in which neither the incumbent president nor the incumbent vice president is running, are similarly bereft of themes. Or, to put it more precisely, neither has a convincing narrative of where we are in history and where we should be headed next.

Successful political parties usually have such narratives. Theodore Roosevelt's Republicans believed in respecting but also regulating private property and in conducting a muscular and assertive foreign policy. This seemed appropriate in a nation that had grown from 5 million to nearly 90 million in the preceding century, that had built the world's largest economy and that had a huge but untapped potential for international power.

Franklin Roosevelt's Democrats believed in government intervention in the economy and a federal safety net, and in using military power to advance freedom and democracy in the world. This seemed appropriate in a nation that had seen its economy collapse but still had the resources to oppose tyranny around the world.

Today's parties lack such narratives. The Democratic Party is all about, well, listen to its rhetoric. It's all about opposing George W. Bush and all his works. But where to go from there?

Domestically, Democrats seem to be reviving the FDR narrative: Expand government to help the little guy. Some thoughtful Democratic strategists argue that although this view was discredited by the stagflation and gas lines of the 1970s, voters are once again ready for more government, and they can cite some poll results in support of that proposition. And it's true that the median-age voter in 2008 will have no vivid memories of the 1970s.

But it's interesting that in resuscitating the FDR narrative, these Democrats -- even Hillary Clinton -- are setting aside the lessons of their party's only successful president of the past 40 years. Bill Clinton was careful to agree that the FDR narrative was obsolete, by backing welfare reform and a balanced budget, and making only incremental progressive changes, like expanding the earned income tax credit. We don't hear such talk today.

On foreign policy, among today's Democrats only Joe Lieberman -- not quite a full Democrat these days -- stays true to the FDR narrative. Instead, the suggestion is that they will get us out of Iraq (although their leading presidential candidates concede that U.S. troops may still be there in 2013) and that with Bush banished to Texas the world will be friends with us again. That ignores the threats that Bill Clinton and Bush grappled with, not always successfully, but at least with an awareness that all was not benign out there.

The Republicans are no better. Many say the party must go back to Ronald Reagan, and the Reagan narrative is at least of recent vintage. Reagan taught that government had grown overlarge and must be cut back and that America must be the assertive champion of freedom and democracy. The problem is that none of the Republican presidential candidates occupy Reagan's place on the political spectrum, and the problems we face are not those that confronted Reagan in 1980.

We no longer have 70 percent tax rates and oil price controls; we no longer face the symmetric threat of Soviet communism. The problem of overlarge government -- the threat that entitlements will gobble up the government and the private economy -- is real but remote. Our foreign adversaries are asymmetric, with a small but worrying potential of inflicting vast damage, and they are not entirely vulnerable to conventional military or diplomatic pressures.

Neither party is presenting a narrative, as the Roosevelts and Reagan did, that takes due note of America's great strengths and achievements. Each seems to take the course, easier in a time of polarized politics, of lambasting the opposition. The Democrats suggest that all our troubles can be laid at the door of George W. Bush. The Republicans, noting Bush's low job ratings, complain about the disasters that will ensue if Hillary Clinton is elected. All these may be defensible as campaign tactics. But it is not a pudding that can successfully govern.