Editor's note: Charles Kaiser is the author of "The Gay Metropolis" and "1968 in America," a former reporter for The New York Times and The Wall Street Journal, and a former press critic for Newsweek.
(CNN) -- President Barack Obama's blockbuster announcement that he is in favor of full marriage equality is the most courageous thing he has done since he entered the White House three and a half years ago.
Coming after his successful strategy to get Congress to repeal don't ask, don't tell so that gays and lesbians can serve openly in the military and the decision of his Justice Department to stop defending the Defense of Marriage Act in federal courts, he has now done nearly as much for gay people as Lyndon Johnson did for African-Americans with the passage of the Civil Rights Act of 1964 and the Voting Rights Act of 1965.
People like me, who were among his most passionate supporters in 2008, felt a sense of gigantic relief. The man who seemed like such a courageous candidate four years ago finally sounded like a genuinely courageous president.
Coming so soon after his decision not to sign an executive order that would have banned discrimination against gays and lesbians among federal contractors, Wednesday's statement instantly obliterated the doubts of millions of his gay supporters.
In some ways, the momentum of his own presidency on gay rights made Wednesday's declaration inevitable. In his interview with ABC News, the president himself cited the end of don't ask, don't tell as one reason he felt compelled to speak out.
"I think about those soldiers or airmen or Marines or sailors who are out there fighting on my behalf and yet feel constrained, even now that don't ask, don't tell is gone, because they are not able to commit themselves in a marriage, at a certain point I've just concluded that for me personally, it is important for me to go ahead and affirm that I think same sex couples should be able to get married," the president said.
Many polls have shown healthy majorities among Americans younger than 30 in favor of marriage equality, and the president noted that even college Republicans who oppose the rest of his policies "are very clear that when it comes to same-sex equality or, you know, sexual orientation that they believe in equality."
The other two facts that probably made his decision easiest were contained in a Gallup Poll released this week, which showed that 65% of Democrats and 57% of independents agree that gay marriage should be legal.
What made the decision most difficult is the closeness of the presidential race in battleground states such as Ohio and North Carolina -- especially after North Carolina residents voted overwhelmingly Tuesday to change the state constitution so that not only marriage but all forms of domestic partnership would be banned for same-sex couples.
The effect on the president's base was immediate and electric.
Andrew Tobias, the long-time treasurer of the Democratic National Committee, said that most "LGBT donors were already willing to focus on all the great stuff that has been done and how much more we'll get done if he's re-elected. But today has ramped up the enthusiasm dramatically. I've gotten calls and five-figure credit card authorizations already from people who were just waiting for this. The enthusiasm level is very high."
Former New York City Mayor Edward Koch is a strong supporter of the president. The dean of New York Democrats also has one of the oldest and strongest records in support of gay rights of any modern American politician, having first come out in favor of the repeal of New York State's anti-sodomy law in 1962.
When informed of the president's action by CNN.com, Koch said, "Someone should write a play about this -- there's so much drama here!"
"The question will be, was he pushed, or are these his real feelings?" Koch continued. "I believe this is how he really feels. I commend him for doing this."
The former mayor pointed out that until today, the president was getting the "worst of both worlds" by continuing to say that his feelings were evolving on this subject.
"He was evolving into dust. And now he has evolved into a major figure who should be thanked by the country."
Among the president's most fervent supporters, a latent fear remains that this announcement could cost him the election. But a new feeling offers gigantic compensation: the conviction that we really did elect a genuinely transformational president.
The opinions expressed in this commentary are solely those of Charles Kaiser.