Bush has called several times, as recently as Saturday, for a federal constitutional amendment to define marriage as the union of a man and a woman. His Democratic rival, Sen. John F. Kerry of Massachusetts, has said he opposes same-sex marriage but does not want to amend the Constitution to ban it.
In 1996, Kerry was one of only 14 senators to vote against the Defense of Marriage Act, which prohibits federal recognition of same-sex marriages. Despite the passage of that act, Bush has said a constitutional amendment is needed because the federal law does not "protect marriage within any state or city" and because it could be struck down by "activist courts."
"If courts create their own arbitrary definition of marriage as a mere legal contract, and cut marriage off from its cultural, religious and natural roots," Bush said Saturday in his weekly radio address, "then the meaning of marriage is lost, and the institution is weakened."
But Lynne Cheney, wife of Vice President Dick Cheney, said Sunday that the states, rather than the federal government, should have the last word.
"When it comes to conferring legal status on relationships, that is a matter left to the states," she said on CNN's "Late Edition," noting that "the constitutional amendment discussion will give us an opportunity to look for ways to discuss ways in which we can keep the authority of the states intact."
Her husband supports a constitutional amendment, though during the 2000 campaign he had said that "people should be free to enter into any kind of relationship they want to enter into. It's really no one else's business in terms of trying to regulate or prohibit behavior in that regard."
The Cheneys' younger daughter, Mary, is a lesbian who has been active in gay issues in Colorado. She now works for the Bush-Cheney reelection campaign.
Californians will not be voting on any marriage initiative this fall, but the state has seen in the past how ballot initiatives can affect candidates on the same ballot. In 1982, Democrat Tom Bradley narrowly lost his bid to become California governor largely because of heavy GOP turnout to vote against a gun control initiative.
Some analysts question whether this year's initiatives will have much effect on voter turnout, if only because turnout is already expected to be high due to intense interest in the presidential race.
In Oregon, a key presidential swing state and one where a marriage initiative will be on the ballot, turnout typically is as high as 80% in a presidential election year, said Tim Hibbitts, an independent pollster in Portland.
With the state's economy ranking among the worst in the country, Hibbitts said, marriage may not be the first thing on voters' minds. But if voting on same-sex marriage helps anyone, it will be Bush, he said.
In Michigan, pollster Ed Sarpolus said that the vote on a marriage amendment this fall may bring out more conservative Republicans, who would vote for Bush, in the closely contested state. But it may also bring out some Catholic Democrats who, though conservative on social issues, are not necessarily Bush supporters.
In Missouri, another swing state in the presidential contest, there was a partisan slugfest over the timing of a vote on a state marriage amendment.
When the Missouri Legislature decided to put the proposed amendment before the state's voters, Republicans wanted it to appear on the November ballot. Democrats, fearing a November vote might also tip the state to Bush, called for the question to appear during the August primary vote.
The issue went to the state's Supreme Court, which sided with the Democrats and set the vote for August.
A fight is still raging over whether the issue will be on the ballot in Ohio, a crucial battleground for Bush and Kerry. Same-sex marriage opponents have until Aug. 2 to gather 317,000 signatures to get a November vote on a constitutional amendment, but advocates have been fighting to keep the issue off the ballot.
Ohio is sympathetic territory for opponents of same-sex marriage. An April poll by the Columbus Dispatch found that 78% of those surveyed thought such relationships should not be granted legal recognition and 60% supported a constitutional amendment to ban them.
National conservative groups have bombarded their members in Ohio with e-mails to promote the amendment. The Human Rights Campaign is investing money and staff in a drive to defeat it. When Bush appeared in Cincinnati recently, the group ran a full-page ad in the local newspaper that read: "Jobs lost in Ohio since 2001: 255,000; Gay marriages in Ohio: 0. Focus on Americans' real priorities, Mr. President."
For activists on both sides of the issue, the challenge in Congress and across the country is to get the attention of themajority of the people who are still trying to figure out their stance on the issue or who do not feel particularly strongly about it.
"People are disturbed by the idea of same-sex marriage, but right now it's just an attitude and not something they are acting on," said John C. Green, a political scientist at the University of Akron who has written on religion and politics. "It's the job of activists to turn those attitudes into votes."
Senate Joint Resolution 40, known as the Federal Marriage Amendment, states: "Marriage in the United States shall consist only of the union of a man and a woman. Neither this Constitution, nor the constitution of any State, shall be construed to require that marriage or the legal incidents thereof be conferred upon any union other than the union of a man and a woman."