The Republican Party's largest gay and lesbian organization is withholding its endorsement of President Bush over the right to marry. 

The Log Cabin Republicans (search) voted last night to hold back their endorsement because of the president's staunch support for a constitutional amendment banning gay marriage. 

The group is calling Bush "disloyal" to its members who supported him four years ago. 

The group is also denouncing John Kerry (search) for what it calls his changing stance on gay and lesbian issues. 

Kerry says he's against a constitutional ban on gay marriages. He also says he supports civil unions.