PolitiFact writers Louis Jacobson, Katie Sanders, Michael McKinney, Sean Gorman, Becky Bowers and Amy Sherman contributed to this article.

This week will be pivotal for the future of marriage in the United States.

On Tuesday, the Supreme Court heard oral arguments on a challenge to California’s Proposition 8, a voter-passed initiative that defines marriage in California as only between a man and a woman.

On Wednesday, the justices will hear arguments on a challenge to the Defense of Marriage Act, a 1996 law that defines marriage as between a man and a woman for the purposes of federal law. DOMA, as it is commonly known, also allows states to refuse to recognize same-sex marriages performed in other states.

PolitiFact has researched several claims involving the marriage issue, including President Barack Obama’s shifting stance on gay marriage. The claims run the gamut, and so do the rulings.

Abbreviated versions of those revisited fact checks are below, and full versions can be found at www.politifact.com/truth-o-meter/. A detailed background of the same-sex marriage debate, key legal issues and possible Supreme Court outcomes is also available on the website.

To comment on our rulings or suggest one of your own, go to our Facebook page (

). You can also find us on Twitter (

).

—————————————

Florida Conference of Catholic Bishops: “In other jurisdictions where (a domestic partnership registry) has been enacted, we have seen that fewer people enter into marriage.”

Michael Sheedy, public policy director of the bishops conference, made this claim last month during a state legislative hearing on domestic partnerships.

Sheedy could offer no examples in the United States to support his statement, and no experts we consulted could find reports that vouch for that effect. In some countries, domestic partnership registries and gay marriage have increased while heterosexual marriage has decreased. But it’s not at all clear that the first trend is causing the second. In other words, correlation does not equal causation.

Marriage is declining in popularity across the world, and has been for decades. No one has shown rates are declining directly because of domestic partnerships.

We rated this statement Mostly False.

————————-

National Organization for Marriage: “Religious groups like Knights of Columbus have been forced to allow same-sex marriage ceremonies in their facilities, against their beliefs.”

Same-sex marriage opposition group National Organization for Marriage made this claim in January in a newspaper ad as the Rhode Island House of Representatives moved toward a vote on legalizing same-sex marriage.

The organization’s regional director cited three examples as proof, but only one involved the Knights of Columbus and it took place in Canada. One of the other examples did not involve a religious group, and no one was forced to take any action in the other example.

We rated this statement Pants on Fire.

————————

Bob Marshall: Homosexual behavior “cuts your life by about 20 years.”

Marshall, a Virginia lawmaker, made this claim last spring in an interview on CNN.

The research Marshall cites to support his claim is two decades old and was conducted near the height of the HIV epidemic. One of the authors said Marshall’s statement is a “gross misrepresentation” of the research. The U.S. death rate from HIV was nine times higher in 1990 than it was in 2010, the latest year for the data.

Marshall cites a number of other studies that show homosexuals face certain health risks. But none of them focused on the life expectancy of homosexuals, and they certainly didn’t conclude that gays die about 20 years earlier than heterosexuals.

We rated Marshall’s statement False.

————————

President Barack Obama: On support for gay marriage.

The president declared his personal support for gay marriage last May in an interview with ABC News.

Obama, a consistent supporter of civil rights for gay couples, nevertheless said as early as 2004 and through 2008 that he didn’t support same-sex marriage. He had written that he believed “that American society can choose to carve out a special place for the union of a man and a woman.” In 2010, he said he wasn’t prepared to reverse himself. But during that May interview, the president said he thought same-sex couples should be able to get married.

On the Flip-O-Meter, Obama earned a Full Flop.

—————————

Vern Buchanan: Says the Obama administration “will no longer enforce the Defense of Marriage Act (DOMA).”

U.S. Rep. Buchanan, R-Fla., made this claim in a March 2011 mailer. The Obama administration said in February 2011 it would no longer defend the law in the courts. But the Human Rights Campaign cited examples that enforcement continues — for example, gay couples can’t file their taxes jointly. We found legal experts who made arguments on both sides about whether not defending DOMA in the courts equals not enforcing it.

If Buchanan had said that Obama would no longer “defend” DOMA, he’d be on safe ground, but he chose “enforce” instead. Still, there’s clear evidence that the Obama administration is seeking to mitigate the law’s effects.

We rated Buchanan’s claim Half True.