In an opinion article in the Columbus Dispatch, Ohio Republican Sen. Rob Portman announced he has changed his mind and now supports same-sex marriage.

He wrote that on learning that one of his sons is gay, he "wrestled with how to reconcile my Christian faith with my desire for Will to have the same opportunities to pursue happiness and fulfillment as his brother and sister."

He is not the only prominent Republican to come to this view in this way. Former Vice President Cheney is another.

And at the Conservative Political Action Conference, a panel sponsored by the Competitive Enterprise Institute drew a large and approving crowd for a discussion labeled "A Rainbow on the Right: Growing the Coalition, Bringing Tolerance Out of the Closet."

It's clear now that support for same-sex marriage crosses party lines. That's what one might expect from polls that show a huge shift of opinion on this issue over the last two decades.

In the early 1990s, large majorities opposed same-sex marriage. In 1996, Bill Clinton didn't hesitate before signing the Defense of Marriage Act, which barred the federal government from recognizing same-sex marriages. He now urges its repeal.

In 2004, after the Massachusetts Supreme Judicial Court by a 4-3 margin discovered that the state's 1780 Constitution required recognition of same-sex marriages, George W. Bush supported the Federal Marriage Amendment, which would bar such marriages across the nation.

That was never going to be ratified, but it did help Bush mobilize tradition-minded voters in states like Ohio in the 2004 election.

Now many polls show majorities or pluralities of Americans favor same-sex marriage. Last November, voters in Maine, Maryland and Washington approved same-sex marriage.

Voters in Minnesota rejected a constitutional amendment that would ban it. That's in contrast to the results in 30 states, all but one of them in 2008 or earlier, where voters approved similar amendments.

Many of those states would surely vote the other way now, including California, whose 52 to 48 percent vote against same-sex marriage in 2008 was overturned by federal trial and appeals courts in a case now before the Supreme Court.

The Supreme Court could rule that the Constitution requires same-sex marriage everywhere. Or it could affirm the appeals court's rationale, which applies to California only.

Or it could say that the Constitution leaves this issue to the states. That's the outcome that, as a supporter of same-sex marriage, I prefer.

Nine states and the District of Columbia have legalized same-sex marriage, most by legislative or popular vote. Eleven other states have no constitutional amendment barring it.

And the 30 states with such constitutional amendments could repeal those amendments by popular vote.

That would require continuing debate and discussion. A good place to start is for everyone to recognize that, as Portman writes, "well-intentioned people can disagree on the question of marriage for gay couples."

I believe that large majorities of people on both sides take their stands out of good motives. Yes, you can find some haters on both sides if you look hard.

But the large majority of Americans believe that their view -- traditional marriage or extension of marriage to same-sex couples -- is or would be good for individuals and good for society.

Backers of traditional marriage can cite hundreds of years of experience and tradition. Backers of same-sex marriage can cite the growing acceptance of gay individuals and couples in all parts of the country.

Those who oppose it fear it will weaken the institution of marriage. But so far I haven't seen evidence that extending marriage to the 3 or 4 percent who are gay has weakened the institution nearly as much as the much larger number of Americans who get divorced or have children without getting married at all.

This is an issue that divides Americans not just on partisan or religious but most conspicuously on generational lines. Young people, including many Republicans, heavily favor same-sex marriage. Elderly people, including many Democrats, heavily oppose it.

If opinion continues to move toward same-sex marriage, it will be a tough issue for Republicans, because most of their voters currently are opposed. But it will be a tough issue for some Democrats as well, because many black voters are staunchly opposed.

But it's an issue we can handle better if we respect and acknowledge the good faith of those on the other side.