OK, everybody may be an exaggeration. Let’s just say every politician of any significance: every presidential candidate, every governor, every member of congress, and the leadership of every party in every house of every state legislature.

Two charts tell you all you need to know about the politics of same-sex marriage. First, it has long-term momentum:

Second, it has the most inexorable kind of momentum there is: generational. Each day a few more supporters turn 18 and a few more opponents die. That’s how it’s going to be for a long, long time.

Explain it to the kids. That’s why President Obama explained his own change of heart this way:

Malia and Sasha, they have friends whose parents are same-sex couples. There have been times where Michelle and I have been sitting around the dinner table and we’re talking about their friends and their parents. And Malia and Sasha, it wouldn’t dawn on them that somehow their friends’ parents would be treated differently. It doesn’t make sense to them and, frankly, that’s the kind of thing that prompts a change in perspective.

This is how taboos fall. One generation genuinely believes in the taboo. The next follows it out of habit, but can’t defend it. And finally there’s a generation that challenges: The kids ask “Why?” and their parents have no answer.

Many of those parents will stay stuck in their ways, but politicians can’t afford to. They have to follow the majority, even if it goes against what they’ve stood for in the past.

We’ve seen this happen before.

Race and the Owens-Louis kids. When Jesse Owens won Olympic gold in Munich in 1936, and then Joe Louis defended his boxing title against Max Schmeling in a sold-out Yankee Stadium in 1938, the rooting wasn’t black vs. white. It was America vs. Nazi Germany.

To many of the white American kids who listened to those two events on the radio, it only made sense to let Jackie Robinson play major league baseball in 1947, and later, to start breaking down color barriers all across society.

When Guess Who’s Coming to Dinner? raised the interracial marriage taboo in 1967, the Owens-Louis kids were the generation in between the Tracy-Hepburn parents and their Sidney-Poitier-dating daughter. They knew interracial marriage was still beyond the pale. Most of them would never consider it themselves. But they couldn’t explain why.

When the Owens-Louis generation reached middle age in the 1970s, segregationist politicians had to capitulate. In 1963 George Wallace could pledge “segregation forever”. In 1970 he successfully ran a race-baiting campaign for governor. But by 1979 he was saying, “I was wrong. Those days are over and they ought to be over.”

The 1970s didn’t end racism — racists can still dog-whistle and use code words — but they ended the days when a politician could stake out an openly racist position and hope to win on it, even in Alabama.

Today, the Owens-Louis kids are the old folks, and returning to Jim Crow is as unthinkable as returning to slavery. Whenever same-sex marriage proponents are allowed to make the link to interracial marriage, the argument is over. No public figure will defend banning interracial marriage — a practice that was controversial even to talk about in 1967.

The Willow-Tara generation. In its acceptance of gays and lesbians, sports has trailed the culture rather than leading it. The characters who changed our thinking about homosexuality are more likely to be fictional ones we met through TV and movies.

In the late 1970s, it was edgy for Jack even to pretend to be gay on Three’s Company. Gay and lesbian minor characters started appearing on dramas like Hill Street Blues in the 1980s. Tom Hanks won an Oscar for his starring role as a sympathetic gay character in Philadelphia in 1993. From 1998-2006 Will and Grace (cited by Vice President Biden) centered on a gay man’s friendship with a straight woman.

I decided to symbolize this generation with a fictional same-sex couple almost exactly the age of the oldest Millennials: Willow and Tara on Buffy the Vampire Slayer, whose relationship began right around the turn of the millennium.

Earlier pop-culture characters got viewers sympathizing with the problems of gay and lesbian individuals and their same-sex relationships. But for most of two seasons Willow and Tara raised a different question: What if there is no problem? What if two people of the same gender meet and fall in love and are happy together?

Like Willow and Tara, the oldest Millennials are about 50 years younger than the Owens-Louis kids. So as a guess, let’s set the 2020s as the decade of capitulation on gay rights: Every major politician will either leave the business or have a change-of-heart by 2030. Even conservatives, even in the Bible Belt.

Remember the Dixiecrats. Does that seem unthinkable? What about Sarah Palin, Rick Santorum, and younger politicians who seem eager to follow their lead? But what about Strom Thurmond, who during his Dixiecrat presidential campaign of 1948 said:

that there’s not enough troops in the army to force the Southern people to break down segregation and admit the Negro race into our theaters, into our swimming pools, into our homes, and into our churches.

In 1971 Senator Thurmond integrated his staff, and in 1983 he voted to honor Martin Luther King with a federal holiday. The sincerity of his transformation may be dubious, but he had to make it.

Biden first. The leading edge of gay-rights capitulation is in the Northeast and among Democrats. So it’s no coincidence that President Obama was put on the spot by Vice President Biden. Whatever happens in 2012, Biden is looking down the road to the Democratic primaries of 2016. No way a Democrat with an ambivalent gay-rights position wins in New Hampshire (where same-sex marriage is already legal) in 2016.

Politicians can read trend lines. If you hope to win statewide office in the Northeast or in California in 2020 — or anywhere in 2030 — you can’t be against same-sex marriage. The question isn’t whether you’ll change, it’s when.

The ancient ship Homophobia has had a long run, but it is going down. While it may take years to sink completely, no politician wants to go down with it. Those with any sense are already checking the exits and plotting their departure.