Senate supporters of a constitutional ban on gay marriage are very unlikely to find the required 67 votes to pass the measure tomorrow; they may not even come close.

A lack of support is usually enough reason for a senator to avoid a vote and a loss. But, except for a fervid few organizations, the gay-marriage vote is not about winning or altering the Constitution. It is about identifying and encouraging a base of voters.

This is not news, but it is important because of the amount of work the Senate has before it – no budget and all the spending bills. An intelligence community in need of major reform. Unsustainable Medicare. The war in Iraq. The deficit. Take your pick. The doomed vote tomorrow tells the public that, for some Senate leaders, firing blanks in the culture wars is more important to them than getting the work of the government done.

Worse, this being an election year, the Senate is scheduled to adjourn Oct. 1, after having all of August off. The schedule was so tight just a couple of weeks ago that Majority Leader Bill Frist gave up on negotiating pay-as-you-go budget rules with moderates. Paygo was abandoned because a compromise was thought hopeless and time was running short. The constitutional ban on gay marriage is certainly hopeless but is scheduled anyway.

It isn’t clear whether the ban will be voted on directly or travel through a labyrinth of procedural votes first, but in either case there will be speeches for and against. Those opposed to the ban will say the Defense of Marriage Act, which defines marriage for federal purposes as an act between one man and one woman and exempts states from observing gay marriages from other states, is sufficient to protect the institution. The positions of Sens. Olympia Snowe and Susan Collins lean on DoMA.

Those in favor of the ban, if they follow the scripts from the organizations demanding it, will argue simultaneously that gays make up only a tiny portion of the U.S. population, perhaps 2 percent – not 10 percent as popularly supposed – but that to allow them to marry would undermine society’s conception of marriage.

Whether society’s conception of marriage should be undermined and made more inclusive is not the question in the Senate, however. The question is whether, as the election nears, the president and Senate leadership can use the issue both to show that they tried to protect marriage and to show that some senators (John Kerry) opposed them.

Debates over anything to do with homosexuality can produce animosity toward gays – recall Maine’s gay-rights votes – and it is unfortunate that this animosity could be generated over a particularly meaningless vote.

The Senate may be too busy to worry about that, however. Its agenda is full for the rest of the year with issues that directly affect millions of Americans. Wednesday’s vote is something else.