"We're going to be racking up more courts of appeals decisions, and every one we get puts more pressure on the Supreme Court to weigh in," said Douglas NeJaime, a law professor at the University of California-Irvine. "It's very likely the Supreme Court ultimately settles this question. Given how quickly things have moved, it's hard for the court to avoid this in the short term."
A three-judge panel of the 6th U.S. Circuit Court of Appeals in Cincinnati will hear arguments from attorneys in six cases from Kentucky, Michigan, Ohio and Tennessee, all Wednesday, the most of any federal appeals court so far.
Similar arguments are set for Aug. 26 in the 7th Circuit in Chicago, for bans in Wisconsin and Indiana, and for Sept. 8 in the 9th Circuit in San Francisco, for bans in Idaho and Nevada. The 5th Circuit in New Orleans is expected to soon set a date to hear arguments on Texas' ban.
The flurry of arguments means an upcoming spate of rulings, possibly all issued this autumn, that could profoundly alter the nation's marriage laws.
If the four federal circuit appeals courts rule in favor of gay marriage, then nine states with pending appeals stand to have their bans stricken down altogether or ordered to recognize out-of-state gay marriages: Ohio, Michigan, Tennessee, Kentucky, Texas, Indiana, Wisconsin, Idaho and Nevada, though the decisions likely would be put on hold for a Supreme Court ruling.
Five additional states under those four circuit courts have gay marriage lawsuits awaiting decisions by federal judges: Alaska, Arizona, Louisiana, Mississippi and Montana.
Observers say the 6th or 5th circuits could deliver the first victory for gay marriage opponents.
The three judges at the 6th Circuit set to hear gay marriage arguments Wednesday are Jeffrey S. Sutton and Judge Deborah L. Cook, both George W. Bush nominees, and Martha Craig Daughtrey, a Clinton nominee.
Among them, Sutton is considered to be the least predictable.
In 2011, he shocked Republicans when he became the deciding vote in a 6th Circuit ruling that upheld the Obama administration's health care overhaul.
"This is the kind of thing where you could see the conservative with a libertarian bent coming out in favor of gay marriage, but who knows?" said Mark Tushnet, a constitutional law professor at Harvard. "Having done Obamacare and maybe screwed his own chances for the Supreme Court, Sutton may feel liberated to do what he thinks is the right thing and go for marriage equality, or he may try to rehabilitate himself and go against it."
Carl Tobias, a law professor at the University of Richmond, said he could see the 6th ruling in either direction, considering Sutton's unpredictability.
Still, opponents of gay marriage likely could rely on the 5th Circuit to give them a win. The court is heavily conservative, and the odds of a majority or full panel of Republican nominees is much likelier there.
Plaintiffs in the 6th Circuit case include a Cincinnati man who wants his dead husband listed as married on his death certificate so they can be buried next to each other in a family-only plot, and a Knoxville, Tennessee, couple who say they want to both be listed on their newborn daughter's birth certificate.
Gay marriage supporters, including former Ohio Gov. Ted Strickland, are holding a rally Tuesday at a downtown Cincinnati park. More rallies by supporters and opponents are expected outside the courthouse Wednesday.