Every now and then, it's fun to watch a cage match between Democrats instead of Republicans.

In one corner stands Andrew Cuomo, governor of New York and potential candidate for president; in the other, Bill de Blasio, the new mayor of New York.

In the governor's budget unveiled this week, Cuomo promised to fully fund universal pre-kindergarten in New York, trumping de Blasio's central campaign promise to do the same for New York City. The difference is that Cuomo, while not specifying the funding mechanism, says his budget will lower taxes and pay for pre-K; de Blasio's plan emphatically called for raising taxes on the rich to cover the expansion.

If you're wondering why the two couldn't just get together and announce a joint proposal, the answer is that both men seem to have political reason to emphasize their differences.

Cuomo wants to tout a record as a governor who is fiscally responsible but progressive, while the mayor seems to want to make good on his campaign promise to make the wealthy pay. De Blasio appeared flat-footed in his reaction to Cuomo's proposal, saying it wasn't good enough because it didn't lock in the funding.

At another level, the Cuomo-de Blasio rift could signal a deeper rift in the Democratic Party between its centrist and liberal wings, between those who view the party's success as based on appealing to moderates and those who think the issue of income inequality has fundamentally shifted the debate to the left. Yet it would seem, in this instance, that the governor has outwitted the mayor. He is offering to implement the mayor's promise.

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Is a tax increase more important to the mayor than universal pre-K? That would be shaky ground on which to fight, even for the nation's newest liberal icon.

The writer is a co-host of The Insiders blog, offering commentary from a Democratic perspective, and was the chief strategist for the Gore 2000 presidential campaign.