Cheered by conservative supporters, President Bush gave a push Monday to a constitutional amendment to ban same-sex marriage as the Senate opened debate on an emotional, election-year measure that has little chance of passing.

President Bush acknowledges a member of the audience as he speaks about a ban on gay marriage at the Eisenhower Executive Office Building Monday, June 5, 2006, in Washington. President Bush rallied support for a ban on gay marriage Monday as the Senate opened a politically charged, election-year debate on a constitutional amendment to prohibit same-sex weddings. [AP]

"Our policies should aim to strengthen families, not undermine them," Bush said in a speech. "And changing the definition of marriage would undermine the family structure."

All Senate Democrats, except Ben Nelson of Nebraska, oppose the amendment, and critics say Bush's efforts are primarily aimed at energizing conservative voters for the November elections. Together with moderate Republicans, the Democrats are expected to block a yes-or-no vote, killing the measure for the year.

"This proposed constitutional amendment is being used to satisfy the most extreme right-wing supporters and politicians," said Sen. Patrick Leahy (news, bio, voting record), D-Vt. "The Constitution is too important to be used for such a partisan political purpose."

Sen. Wayne Allard (news, bio, voting record), R-Colo., who sponsored the measure, acknowledged that politics played a part in the timing of the debate, but for a different reason: to force senators to take a stand and answer for their votes on the campaign trail.

"We ought to have a vote on the amendment every year," Allard said.

The amendment would prohibit states from recognizing same-sex marriages. To become law, it would need two-thirds support in the Senate and House, and then would have to be ratified by at least 38 state legislatures.

The White House played down the significance of the 10-minute presidential event, saying Bush was simply speaking out on an issue being debated on Capitol Hill. Press secretary Tony Snow said the president was not personally lobbying senators to pass the amendment.

Bush also pressed for it in his radio address on Saturday.

"I'm not sure this is a big driver among voters," Snow said.

Bush said a constitutional amendment is needed because laws that state legislatures have passed defining marriage as being between a man and a woman are being overturned by a few judges.

"When judges insist on imposing their arbitrary will on the people, the only alternative left to the people is an amendment to the Constitution ¡ª the only law a court cannot overturn," the president said.

Bush also rebuffed critics who argue that the amendment conflicts with the GOP's opposition to government interference and the importance of states' rights.

"A constitutional amendment would not take this issue away from the states, as some have argued," Bush said. "It would take the issue away from the courts and put it directly before the American people."

First lady Laura Bush said recently that while Americans want to debate the issue, "I don't think it should be used as a campaign tool."

Vice President Dick Cheney, whose daughter, Mary, is a lesbian, splits with Bush on the issue. Cheney said he thinks Americans should do everything they can to accommodate any type of relationship, and that there should not necessarily be a federal policy in this area.

Human Rights Campaign President Joe Solmonese said Bush was favoring an amendment that would give Americans license to discriminate against homosexuals.

"The fact that he's out of step with the first lady and the powerful vice president tells me who he's answering to today," Solmonese said.

More than half of Americans, 58 percent, said in an ABC News poll released Monday that same-sex marriages should be illegal. But only four in 10 said they support amending the Constitution to ban gay marriage, while a majority said states should make their own laws on gay marriage.

With Bush taking center stage on the issue, advocates on both sides of the issue rushed to comment.

On the left, Caroline Fredrickson, director of the ACLU legislative office in Washington, said lawmakers rightly rejected the amendment in 2004 and should do so again. "Discrimination has no place in America, and certainly not in our founding document," she said.

On the right, Matt Daniels, president of the Alliance for Marriage, argued that same-sex marriage advocates are trying to circumvent the democratic process and redefine marriage through the courts. "Marriage is the social glue that unites the two halves of the human race to share in the enterprise of raising the next generation," Daniels said.