After years of winding through the courts, two definitive cases in the marriage debate will finally reach the Supremes. Here's what they'll be considering.

Jonathan Ernst / Reuters

WASHINGTON — The line began last Thursday. In a clear sign that the two cases that will be brought before the Supreme Court this week represent a historic moment in the fight for marriage equality, people began lining up outside days ago in hopes of nabbing a seat in the courthouse while justices consider the constitutionality of California's Proposition 8, and the Defense of Marriage Act. The cases have been winding through the courts since 2009, and every court to hear the challenges since then has sided with proponents of marriage equality. Now, however, the cases have reached a closely divided Supreme Court, and all eyes — and ears — this week will be on the nine justices. tl;dr: Oral arguments in the Proposition 8 case are slated to begin at 10 a.m. Tuesday, are set to last an hour, with audio and transcript to be released by 1 p.m. Oral arguments in the DOMA case are slated to begin at 10 a.m. Wednesday, are set to last an hour and 50 minutes, with audio and transcript to be released by 2 p.m.

First up is California's Proposition 8 on Tuesday. Jason Merritt / Getty Images Plaintiffs Sandy Stier (left) and Kris Perry.

On Tuesday, the justices will consider whether the 2008 amendment to California's constitution banning marriage for gay couples is allowed under the U.S. Constitution. Prior to the statewide vote that narrowly passed the amendment, the California Supreme Court had ruled that the state's constitution required that same-sex couple be allowed to marry. Proposition 8 ended that right, but about 18,000 couples married during the interim. The justices also will be deciding, as a preliminary matter, whether the proponents of Proposition 8 — the people who put the measure on the ballot — have the right to take the case to the Supreme Court. Normally, it would be the government of California defending the law. In this case, however, none of the state officials — now led by Gov. Jerry Brown and Attorney General Kamala Harris — have been willing to defend the law. As such, the proponents, who have some legal rights under California law, have been defending the measure. If the justices decide the proponents don't have the right to appeal the case, then the Supreme Court won't decide the ultimate question of whether the law is constitutional. This would mean the trial court judge's decision striking down the law stands, but it would not apply outside the state (and some have questioned whether it would even apply to the whole state).

Beyond the standing question, the justices will be considering whether the constitutional right to marry extends to same-sex couples, an argument that will be made by Ted Olson — President George W. Bush's former lawyer at the Supreme Court. Olson has argued both that the fundamental right to marriage applies to gay couples and also that treating same-sex couples differently than opposite-sex couples violates the Constitution's equal protection clause because it is sexual orientation discrimination. It is in this latter argument that one of the key questions is to be presented to the justices: Should courts view laws, like Proposition 8, that classify people based on sexual orientation more skeptically? Heightened scrutiny, as it is called, is what courts use to examine laws that classify people based on race, religion or sex. When deciding whether heightened scrutiny should apply, courts consider several factors, including any history of discrimination, the group's relative political powerlessness, the centrality or immutability of the characteristic in question, and the relationship between the characteristic and the individual's ability to contribute to society. The lawyers opposing Proposition 8 argue that laws that ban same-sex couples from marrying should be subjected to heightened scrutiny and, accordingly, found unconstitutional. Even under the lowest level of scrutiny, called rational basis, Olson will argue that Proposition 8 should nonetheless be found unconstitutional. The justices also will be hearing arguments from President Obama's Supreme Court lawyer, Donald Verrilli Jr., who weighed in on behalf of the two same-sex couples' claims recently. The government did not go so far as to argue that the court should strike down all bans on same-sex couples' marriages, instead focusing on the California case before the court. Verrilli noted, however, that the argument the government is advancing also could impact other states that grant similar rights to same-sex couples through civil unions or domestic partnerships but "still restrict marriage to opposite-sex couples": Colorado, Delaware, Hawaii, Illinois, Nevada, New Jersey, Oregon, and Rhode Island. This "nine-state solution" has been pointed to be some as a middle-ground option for the justices. The most narrow solution would involve basing the decision on the fact that same-sex couples in California were allowed to marry, and Proposition 8 ended that. California is the only state to have done so, and the Ninth Circuit Court of Appeals held that such action rendered the measure unconstitutional. If the Supreme Court agreed with that logic, therefore, it's unlikely that any other state would have its laws immediately impacted. Arguing in favor of Proposition 8 will be Charles Cooper, whose primary argument has revolved around showing that the state has an interest in keeping marriage limited to opposite-sex couples in order to encourage "responsible procreation." In other words, because gay and lesbian couples cannot have a baby without planning it, they don't need the encouragement to "responsible procreation" that marriage provides. The proponents also have argued to the court that "it is plainly reasonable for the People of California to be concerned about the potential consequences" of allowing same-sex couples to marry. A ruling that Proposition 8 is constitutional would mean that the amendment would stay on the books, but, more broadly, it also would be a striking loss to LGBT advocates, who were cautious about the Proposition 8 challenge in 2009 but have increasingly felt that momentum since this past November has made their cause inevitable.

Damian Dovarganes, File / AP Lawyer Ted Olson (right) with plaintiffs Jeff Zarrillo (left) and Paul Katami (middle).

Second up is the Defense of Marriage Act on Wednesday. Macey Forondo Plaintiff Edith Windsor.

On Wednesday, the justices will be hearing the second case: the challenge to section 3 of the Defense of Marriage Act. The portion of the 1996 law in question defines "marriage" and "spouse" in federal law as only including marriages between one man and one woman. Although no states allowed same-sex couples to marry when the law was passed, today the law prevents same-sex couples whose marriages are recognized by their states from having those marriages recognized by the federal government. In Edith Windsor's case, that meant a hefty estate tax bill when her wife, Thea Spyer, died. Had Spyer been a man, Windsor would have been exempt from paying the tax. Although Windsor sued the federal government to get the taxes refunded to her because she argues DOMA is unconstitutional and she should not have had to pay the tax, she is in the unusual position of having the federal government on her side. In February 2011, Attorney General Eric Holder informed House Speaker John Boehner that Obama and Holder had concluded that heightened scrutiny should apply to sexual orientation-based classifications and that, accordingly, DOMA should be found unconstitutional. As such, Holder said the Justice Department would no longer be defending challenges to DOMA in court. Boehner took a vote of the House Bipartisan Legal Advisory Group (BLAG), which the Republican majority controls 3-2, and took up the defense of the law.

As in the Proposition 8 case, the court has asked the parties to address whether the case should even be heard by the Supreme Court. In the DOMA case, the justices went so far as to appoint a Harvard Law School professor — Vicki Jackson — to argue that the court has no jurisdiction to hear the case. They've also expanded the argument time and split it in two, giving 50 minutes first to discussion of the procedural issues. Jackson has argued that BLAG does not present a sufficient "injury" that it would suffer if DOMA is struck down in order to find they have the required constitutional standing to bring the appeal. She also noted that BLAG only represents the House and, therefore, can't be arguing that it represents the views of Congress. Regarding the Obama administration's decision to stop defending the law, Jackson argues that there is no longer a "case or controversy" because the administration is taking Windsor's side in the case and won in the court below. In response, the two government entities submitted opposing briefs and will be arguing opposing positions on Wednesday. Deputy Solicitor General Sri Srinivasan from the Department of Justice will argue that "the President's direction that the Executive Branch continue to enforce Section 3, notwithstanding his legal arguments, creates just as much of a ... controversy on appeal as in the district court." DOJ argues, however, that BLAG does not have standing, for many of the same reasons given by Jackson. BLAG is represented by Paul Clement — another of Bush's former Supreme Court lawyers — who will be presenting the opposite arguments. BLAG asserts instead that "[t]he House certainly has a concrete interest in ensuring that its passage of DOMA is not completely nullified by a binding judicial determination," which should lead the court to find that BLAG has standing. BLAG then goes on to argue that if it does not have standing, there is no controversy that the court would have jurisdiction to resolve.

Then, the court will taking an hour to consider the "merits" argument about whether Section 3 of DOMA is constitutional. The appeals court to consider Windsor's case determined on a 2-1 vote that heightened scrutiny applies to sexual orientation classifications and that, applying that standard, "Section 3 of DOMA violates equal protection and is therefore unconstitutional." BLAG's lawyer, Clement, will be arguing that heightened scrutiny should not apply to sexual orientation. BLAG also will be seeking to advance its argument that DOMA was a "line-drawing" exercise in which the government took a properly cautious step to preserve "uniformity" and the status quo while states were left free to experiment and resolve the debate over how same-sex couples' relationships should be treated under the law. The Department of Justice's Verrilli will be arguing, as the appeals court concluded, for application of heightened scrutiny here and that, under that standard, DOMA is clearly unconstitutional. In its brief, the administration also argued that if the court decides that heightened scrutiny should not apply, DOMA "would uniquely qualify it for scrutiny under an approach that calls for a measure of added focus to guard against giving effect to a desire to harm an 'unpopular group.'" Windsor argues that DOMA is unconstitutional regardless of the standard applied. Her lawyer, Roberta Kaplan, argued to the court in an earlier filing that BLAG's given reasons to justify passage of DOMA "fall into three general categories: (1) procreation-related interests, (2) uniformity/conservation of resources interests, and (3) interests in dual sovereignty, tradition and caution. None provides a rational basis for DOMA."

The Court does not allow video recordings of the arguments, but it will be releasing audio of the arguments, as well as a transcript, on the day of each argument.

Then, the justices will meet privately to discuss the cases and cast their tentative votes. Larry Downing / Reuters