Now is the time for President Obama to complete his evolution on the subject of same-sex marriage.

Supporting the right of all Americans to marry the person of their choice would be the right thing to do. Strange as this may sound, it might also be good politics.

More to the point, it would not be the almost certainly disastrous political move it would have been even in the last presidential campaign, when none of the major Democratic candidates supported the right to marry.

Flash forward three years to Hillary Clinton’s remarks this week. “Gay rights are human rights, and human rights are gay rights,” declared Obama’s chief primary rival and now his secretary of state, echoing her famous declaration, as first lady, about women’s rights. Clinton did not go so far as to endorse same-sex marriage. Yet the arc of her logic bends inexorably in that direction. As Clinton surely knew when she proclaimed that “no practice or tradition trumps the human rights that belong to all of us.”

Madame Secretary, recall the joy you experienced at your daughter’s wedding. If she were gay, should she — should you? — have been denied that moment?

The president has been edging ever closer to supporting same-sex marriage but hasn’t taken the plunge. He called for the repeal of the Defense of Marriage Act. He refused to defend its constitutionality in court.

He has moved from opposition (“I believe that marriage is the union between a man and a woman,” at pastor Rick Warren’s Saddleback Church in 2008) to evolution. “I’m still working on it,” he told ABC News in October.

The president’s most recent opportune moment to make the Darwinian leap came when his attendance at a fundraiser attended by gay Democratsin New York inconveniently coincided with the state’s impending vote on same-sex marriage. New York did the right thing. Obama ducked.

Now, in a memorandum to Democratic consultants and campaign managers, gay rights advocates argue that backing same-sex marriage is not the political poison it was in years past. Indeed, they contend, it could be a political boon — not only with Democrats but with independent voters, some 56 percent of whom approve of same-sex marriage.

Their data? Analysis by Joel Benenson, Obama’s pollster, and Jan van Lohuizen, who served that role for George W. Bush.

“What was once used as a wedge by Republicans to turn out conservatives and put Democrats on the defensive may now have the opposite effect, as growing numbers of voters across the board support the freedom to marry,” says the memo, written by Democratic strategist Doug Hattaway and Evan Wolfson president of Freedom to Marry.

In particular, Hattaway and Wolfson note, “Younger voters, who are critical to Democratic victories in 2012, are highly motivated by candidates who show their support for ending discrimination in the nation’s marriage laws.” Hear that, Mr. President? Younger voters!

Support for same-sex marriage is accelerating; it rose by about one percentage point annually between 1996 and 2009 and shot up another 10 points in the two years since to 53 percent.

As significant: Intensity is on the side of marriage equality. More voters strongly support same-sex marriage than oppose it. And the strongly opposed minority is unlikely to back Democratic candidates no matter what.

Could Obama, accused Kenyan secular socialist redistributor of wealth, safely come out for same-sex marriage months before an election that, even if he wins, promises to be excruciatingly close?

The ordinary rules of the political playbook counsel the more conservative course: Don’t rattle the middle, don’t open up a new front on social issues. The latest ad from Texas Gov. Rick Perry accuses Obama of waging a phantom “war on religion.” Why offer fodder?

And sticking out the presidential neck seems especially risky in the current economic environment, when voters want Obama focused on the economy, not distracted by social engineering.

The understandable instinct of the president and his political advisers is to play it safe. But the data ought to give comfort that Obama would not commit political suicide were he to complete the evolution he clearly knows is inevitable. In the politics of 2011, survival of the fittest does not compel opposition to marriage equality.

And then there is this question for Obama: Mr. President, what better moment will there be? You might lose. A lame-duck proclamation would be lame. If not now, when?