President Bush and his likely Democratic challenger, Senator John Kerry, both say they oppose same-sex marriages, but they differ on how the issue should be handled by the government.
President Bush has called on Congress to pass a proposed constitutional amendment that would define marriage as a fundamental institution between a man and a woman and ban gay marriages.
But, the president says states should be free to make their own choices in establishing legal arrangements other than marriage - such as allowing civil unions - that provide legal protection for homosexual couples.
Mr. Kerry says he also opposes legalizing gay marriage, but he has criticized President Bush's call for a constitutional amendment banning it.
The Massachusetts senator says he is a believer in civil unions because they provide equal legal protections for gay couples. Mr. Kerry says states should be able to decide on their own legal arrangements for same-sex couples.
The debate over gay marriages was unleashed earlier this year, when the Massachusetts supreme court ruled that banning same-sex marriages is unconstitutional.