In 2004, when Wisconsin Right to Life sponsored radio ads urging people to contact the state's senators, it was trying to stop filibusters against judicial nominees. In 2002, when Joseph Frederick, an 18-year-old high school senior, held up a "Bong Hits 4 Jesus" banner at an Olympic torch rally in Juneau, Alaska, he was, by his own account, only trying to get on TV.

Yet both cases, which resulted in Supreme Court decisions announced on the same day this week, illustrate the perils of carving out exceptions to the First Amendment. Rationales for censorship tend to expand and proliferate, leaving people uncertain about whether they're free to speak their minds.

Because Wisconsin Right to Life's anti-filibuster ads mentioned a senator who was running for re-election that year, they ran afoul of the Bipartisan Campaign Reform Act. That law prohibits corporations, including nonprofit interest groups, from sponsoring TV or radio spots that mention a candidate for federal office close to an election.

This astonishing rule against criticizing politicians flowed logically from the post-Watergate effort to prevent official corruption by restricting campaign donations. The attempt to purify politics led to restrictions on independently financed campaign ads that might replace direct contributions, which led to restrictions on "sham issue ads" that could help elect or defeat a candidate without explicitly telling people how to vote.

Although the Supreme Court ruled four years ago that the latest restrictions were not unconstitutional on their face, it has now held that applying them to the Wisconsin Right to Life spots would violate the First Amendment. "A court should find that an ad is the functional equivalent of express advocacy," the majority said, "only if the ad is susceptible of no reasonable interpretation other than as an appeal to vote for or against a specific candidate."

Since the Court has not simply overturned the restrictions, we can look forward to litigation aimed at defining which ad interpretations are reasonable. In the meantime, interest groups seeking to participate in political debates still will have to think twice before they speak.

There's a similar problem with the rationale endorsed by the same five justices in upholding a public school principal's decision to tear down Frederick's "Bong Hits 4 Jesus" banner and suspend him. Since students were let out of class to watch the Olympic torch relay (although Frederick himself came directly from home), the Court ruled, they were still under school supervision, and the principal was within her rights to take down the banner because it violated the school's anti-drug policy.

"Schools may take steps to safeguard those entrusted to their care from speech that can reasonably be regarded as encouraging illegal drug use," the majority said. In contrast with, say, a general rule against banners at school events, this topic-specific, viewpoint-based ban encourages suppression of dissenting opinions.

While students in school do not have the same First Amendment rights as adults, the Supreme Court has emphasized that they do not "shed their constitutional rights to freedom of speech or expression at the schoolhouse gate." That's why two of the justices who ruled against Frederick said in a concurring opinion that the Court's new rationale for censorship should apply only to pro-drug speech, as opposed to political or social commentary.

But this distinction may be hard to maintain in practice. Imagine a student who attacks the war on drugs by arguing that there's nothing inherently wrong with smoking pot, or by sharing accurate information about the relative hazards of marijuana and alcohol, or by noting New York City Mayor Michael Bloomberg's un-Clintonian response to the question of whether he'd ever smoked cannabis: "You bet I did, and I enjoyed it."

In each example, the student, though engaged in political debate, "can reasonably be regarded as encouraging illegal drug use." Will his speech be protected anyway? Like the activist with an issue ad, he can't be sure.