Robert Samuelson's new column on the candidates is very good, as usual.

For the party faithful, this is a sweet moment. They have their candidates and, whatever the obstacles, can still imagine victory in November. But the rest of us ought to remember that the politics of winning and governing often collide. The first involves maximizing popularity. The second requires farsighted choices that ultimately benefit the country but may initially hurt a president's approval ratings. What have we learned about the candidates' capacity for governing? Enough, I think, to temper the excitement.

He finds plenty of fault in both candidates, and concludes by reminding readers of the case for divided government.

For me, McCain does have one provisional and accidental advantage. By most appraisals, the Republicans will get slaughtered in the congressional elections, and I have a visceral dislike of one-party government. It didn't work well under Bill Clinton or George W. Bush. Divided government doesn't ensure good government, but it may limit bad government by checking the worst instincts of both parties.

It is a point that my National Journal colleague Jonathan Rauch has argued persuasively from time to time. See this piece from 2006 [pdf]:

In a complicated world, good policy is usually bound to be eclectic; in an unpredictable world, successful policy-making depends on correcting errors. Eclecticism comes from compromise, error-correction from coherent criticism. One-party rule seems to short-circuit both mechanisms.

Politicians compromise because they have to, not because they like to. Divided government forces them to compromise as a fact of daily life. Although compromise does not guarantee sound or successful policy-making, it does draw both parties toward the center and produce bipartisan buy-in. It's no coincidence that divided government produced the 1986 tax reform and the 1996 welfare reform, the great reforms of their respective eras.

Two-party rule also helps to marginalize partisan extremists and curb ideological excess. The Democratic Congress moderated President Reagan's unsustainable tax cuts and defense buildup, safeguarding his legacy. In the Clinton era, divided government produced a miraculously frugal fiscal detente. Ronald Reagan and Bill Clinton both succeeded not in spite of divided government but because of it.

The idea is not yet much talked about in 2008. The Democrats seem certain to rule Congress with expanded majorities, yet I don't see many independents (Samuelson aside) arguing that this inclines them to prefer McCain. Come to think of it, why am I not (yet) advancing that argument myself? Good question. I'll have to get back to you.