Give the Democratic candidate for governor, Attorney General Spitzer, some credit for skipping this morning’s event calling for “smaller class sizes” — i.e., more dues-paying members for Randi Weingarten’s United Federation of Teachers. But don’t give him too much credit; his running mate, Senator Paterson, will be there, marking the first day of school by pledging fealty to the union’s agenda.

This conveniently lets Mr. Spitzer have it both ways. He can signal to the taxpayers by his absence that he isn’t the union’s pawn on education policy, but he can signal to the union by the presence of his would-be lieutenant governor that he is the union’s pawn on education policy.

It’s not the first time Mr. Spitzer has attempted such a straddle. On the Campaign for Fiscal Equity lawsuit, he’s been in court as attorney general defending the state’s taxpayers against the effort to wring from them an addition $23 billion for New York City’s public schools. Those schools are already extravagantly funded, yet yield for the most part middling to poor results. Yet on the campaign trail, he’s been promising that as governor, he’d spend those additional billions — while also promising not to raise taxes.

Given the messianic tone of Mr. Spitzer’s campaign commercials, we wouldn’t be surprised if some voters are under the impression that Mr. Spitzer can turn thin air into billions of dollars. But if Mr. Spitzer ends up as governor — and particularly if his party also controls the state Senate and assembly — he will find that these issues are harder to finesse in office than on the campaign trail. He’s going to have to either keep or break his promise not to raise taxes and deliver or fail to deliver on his promise of billions more in taxpayer money for the city’s schools. The straddle can only go on for so long.