Hillary Rodham Clinton took to Twitter on Tuesday to make her first direct comments on the same-sex marriage issues now before the Supreme Court -- just as the justices were about to begin hearing the case:

Clinton has said that the "-H" signature indicates a Twitter message written by Clinton herself, as opposed to her campaign aides.  The hashtag she used was a top-trending item on Twitter on Tuesday afternoon.

Her tweet made clear that the newly announced Democratic presidential candidate is highlighting same-sex marriage as a defining issue. She is also drawing a clear distinction with Republican candidates who have said they oppose gay marriage.

"There are some on the other side, including some who are running for president, who find my relationship intolerable," a Clinton supporter named Jared Milrad wrote in an online message released by the Clinton campaign Tuesday. Milrad and his partner, who appear in the video Clinton released to announce her campaign earlier this month, plan to be married this summer.

[A vexing question for GOP hopefuls: 'Would you go to a gay wedding?']

Although views on same-sex marriage have changed dramatically and legal rights for such marriages may seem inevitable, "it can all be turned back with just one election," Milrad wrote.

Clinton's campaign changed her H-shaped campaign logo on Twitter and Facebook from red, white and blue to a rainbow in symbolic support of the gay couples asking the high court for the constitutional right to marry. Her campaign also tweeted a link to a campaign web video featuring a man in Iowa telling Clinton that he was "thrilled" that Clinton supported what he called marriage equality:

"That's Our Gal," the man tells Clinton, who grins.

Her support for a Supreme Court ruling that would make same-sex marriage a constitutional right had previously come as a statement from the Clinton campaign, rather than from Clinton herself. As recently as last summer, Clinton had said that the state-by-state legal fight to allow gay marriage seemed to be working. Marriage had traditionally been a matter left to states, Clinton said then.

Clinton had long since changed her 1990s view that marriage is between a man and a woman, as well as her 2008 campaign stance in favor of civil unions as an alternative to legal same-sex marriage. But with gay-rights activists now preferring a Supreme Court ruling on constitutional grounds, Clinton has adopted that position as well.