NOW THAT I think about it, there was something noteworthy that occurred at last week's Republican presidential debate. My initial take was the race for the 2008 nomination was unchanged, and indeed it was. But when you compare what was said at the Republican debate with what Democratic presidential candidates said at their debate a week earlier, you discover something interesting. The parties have, in one significant respect, changed places.

Republicans used to be the consensus party, Democrats the coalition party. If you were conservative on most issues, you were in sync with the Republican consensus. Among Republicans, there wasn't much diversity of opinion. As a coalition party, Democrats tolerated a lot of diversity. Each group in the coalition--labor, liberals, feminists, gays, minorities, even a shrinking band of moderates--was free to pursue its separate agenda. Now, however, there's a Democratic consensus, often strictly enforced.

It's true that Democrats remain more diverse than Republicans in the identity group sense. But ideologically, Republicans are more diverse--and more tolerant of diversity. This was not only plainly on display in the two debates, but it's also reflected in national politics more broadly and in congressional debates.

Start with abortion. The eight Democratic presidential candidates were questioned by NBC's Brian Williams about the Supreme Court's decision upholding the ban on partial birth abortion. "Most of the people of this stage put out statements and criticized the ruling," Williams noted, but a majority of Americans approved of it.

Not one of the Democrats voiced qualms about partial birth

Republicans were not as lockstep when asked about abortion--in their case, about Roe v. Wade, the 1973 decision legalizing abortion. Most said they would be delighted if Roe were overturned. But there were permutations. Former Governor Jim Gilmore of Virginia said Roe was wrongly decided, but he stuck to his view that abortion should be legal in the first 8 to 12 weeks of pregnancy. Gilmore calls himself a pro-lifer, but that's not the standard pro-life position.

Rudy Giuliani, the ex-mayor of New York, said it "would be O.K. to repeal" Roe, but "it would be also if a strict constructionist judge viewed it as precedent" and upheld Roe. In other words, he played it both ways. Giuliani said he hates abortion, but then he reaffirmed his support for a woman's right to choose an abortion. "You have to respect a woman's right to make that choice differently than my conscience," he said.

Now, here's the important point. For two decades, Democrats with pro-life leanings have become pro-abortion when deciding to run for the presidential nomination. The party--at least the presidential wing--doesn't tolerate diversity on abortion. It's worth noting that while a few dozen pro-life Democrats are elected to Congress, they remain largely silent on the issue once they get to Washington. Pro-choice Republicans routinely sound off.