In the nearly two years since the US Supreme Court struck down the District of Columbia's ban on handguns, more than 190 challenges have been filed seeking to overturn other gun-control laws or to reverse firearms convictions.

Now, with the justices examining a similar ban in place in Chicago, gun-rights advocates are hoping for another landmark constitutional victory – this time extending an individual right to keep and bear arms in cities and towns across the country. (To see a preview of this case, click here.)

But the ultimate showdown over gun control in America will be waged in a future legal case not yet on the high court's radar, analysts say. At issue in that case: Are Second Amendment rights as fundamental as freedom of speech and religion, or will gun rights be subject to lesser constitutional protection?

The answer to that question – and the potential future course of gun control – may rest with a majority of the nine men and women on the Supreme Court. When that future case arrives, it will all boil down to a three-word phrase of legal jargon: "standard of review."

What does 'standard of review' mean and how does it relate to gun rights?

The way the Supreme Court protects individual constitutional rights against encroachment by the government is by weighing the government's interest in a particular law against the individual right preserved in the Constitution.

For example, when the government passes a law censoring people from engaging in core political speech, the court requires the government to demonstrate it has a compelling interest in the censorship and to prove that the measure is the least intrusive means of achieving that governmental interest. If it can't prove both, the law must be struck down.

Not all rights warrant the toughest level of constitutional protection. In the intermediate level, judges often attempt to balance competing interests to reach the proper outcome.

What standard of review do gun-control advocates want?

The Brady Center to Prevent Handgun Violence has filed a friend-of-the-court brief in the Chicago case urging the justices to establish a standard of review in which judges would be reluctant to overturn gun-control regulations enacted by elected officials.

"Gun policy is best determined as it always has been in this country: in the political arena, without courts second-guessing reasoned legislative judgments," writes Paul Wolfson in his brief on behalf of the Brady Center.

What standard of review are gun-rights supporters seeking?

Many argue that the Second Amendment right to keep and bear arms is a fundamental right that can be limited only in the narrowest circumstances and only when the government demonstrates a compelling reason. "We think the Constitution provides the proper test. It is: 'shall not be infringed,' " said Larry Pratt, executive director of Gun Owners of America, quoting from the amendment. "We think 'shall not' means 'none.' "

Are the Supreme Court's gun cases interconnected?

The court is engaged in what could become a three-step process. The Washington decision in 2008 established that the Second Amendment protects an individual right to keep and bear arms for self-protection in the home.

In the second step, the court will determine whether the Second Amendment applies to state and local governments. The case currently before the court, McDonald v. Chicago, is a challenge to Chicago's handgun ban, which is like the one struck down in Washington. If the high court extends the same Second Amendment protection nationwide, then the third step would involve the court establishing a uniform standard of review to guide lower court judges in assessing which gun-control measures are permitted under the Second Amendment.

What have the justices said about the standard of review in gun cases?

The majority justices addressed this issue briefly in the Washington decision. "Like most rights, the right secured by the Second Amendment is not unlimited," wrote Justice Antonin Scalia.

"Nothing in our opinion should be taken to cast doubt on longstanding prohibitions on the possession of firearms by felons and the mentally ill, or laws forbidding the carrying of firearms in sensitive places such as schools and government buildings, or laws imposing conditions and qualifications on the commercial sale of arms," Justice Scalia said. (For Monitor coverage of the Washington decision, click here.)

This suggests that the majority justices were of the view that some gun-control laws will be subject to a level of intermediate judicial scrutiny. But it's not clear whether that standard will apply in all cases, or whether others will require more rigorous "strict scrutiny."

Why is the standard of review so important?

It is potentially the most significant aspect of the Supreme Court's emerging Second Amendment jurisprudence, because it will determine which gun-control laws will be upheld and which won't.

The Washington decision brought a flood of challenges to gun-control laws, but most were upheld, said Dennis Henigan, vice president for law and policy at the Brady Center. "There has not been a wholesale invalidation of gun laws, with only one exception," he said. That involved a law forcing anyone indicted for child pornography to immediately surrender his or her firearms. Two federal judges invalidated the law because it violated the presumption of innocence.

What record do state judges have when ruling on gun-control measures?

In assessing the constitutionality of gun-control laws, Mr. Henigan said, state judges have placed significant weight on the government's interest in regulating firearms as a means to protect public safety. The Supreme Court should adopt the same rationale, he said.

Mr. Pratt of Gun Owners of America disagreed: "I should be able to carry a firearm wherever and however I want without any never mind from the government," he said.