Now that the Senate Finance Committee has voted for the health-care bill drafted by Montana Democratic Sen. Max Baucus, negotiations over the real bill can begin in Senate Majority Leader Harry Reid's cozy Capitol hideaway. It won't be easy.

Democrats now face a central problem for any governing party: How to pass a major piece of legislation when there are a lot of sharply different ideas about what should be in it. Trying to reconcile what Democrats in the House prefer with what Democrats in the Senate want is already opening up divisions among the party's supporters.

This week, for example, leaders of 30 labor unions called for Democrats to reject Mr. Baucus's bill because it doesn't include the government-run health insurance program better known as the public option....