President Barack Obama on Thursday endorsed state ballot initiatives to legalize same-sex marriage in Washington state, Maryland, and Maine as he sought to galvanize gay and lesbian enthusiasm for his re-election bid.

Statements issued by the Obama campaign in those three states urging voters to approve the gay-marriage measures on their respective November 6 ballots came five months after Obama became the first U.S. president to express support for the right of same-sex couples to wed.

With polls showing Obama and Republican challenger Mitt Romney running neck and neck, the outcome of the race is likely to hinge largely on the Election Day turnout of their core constituencies, and both candidates are doing the utmost to motivate their supporters.

For Obama, the gay and lesbian community is seen as a loyal and potentially pivotal voting bloc, along with larger demographic groups such as Hispanics and single, young women.

"While the president does not weigh in on every single ballot measure in every state, the president believes in treating everyone fairly and equally, with dignity and respect," according to a statement in Seattle by Paul Bell, press secretary for Obama's campaign in Washington and Oregon.