The legal case that gay-rights activists feared to see is about to get under way in a federal courtroom in San Francisco. For the next several weeks, plaintiffs will argue that the U.S. Constitution forbids states from restricting marriage to one man and one woman. The case has brought together some of the most powerful appellate attorneys in America but has divided gay-rights lawyers and legal scholars who fear that even if successful, the case could set the issue on a collision course with a less-than-sympathetic U.S. Supreme Court.

The high court has issued powerfully pro-gay-rights decisions at key points in the past 20 years — including striking down criminal statutes forbidding gay sex six years ago. But it has never voiced a word of enthusiasm for gay marriage. That has left scholars and longtime legal veterans of the gay-rights movement fearing disaster for gay marriage, should the issue be decided by the conservative-leaning Justices. "When I try to count the votes in favor of same-sex marriage on the Supreme Court, I have trouble getting to one," Andrew Koppelman, John Paul Stevens Professor of Law at Northwestern University, told TIME.