It’s been 20 years since a pipe bomb sent to federal Judge Robert Vance’s Alabama home killed him and injured his wife.

It’s been more than 30 years since a hired killer gunned down federal Judge John H. Wood Jr. in his San Antonio driveway.

It’s been 10 days since a New Jersey jury deadlocked on whether a radio shock jock and blogger should be convicted for saying three federal appeals court judges in Chicago deserve to be killed.

You might think that getting a conviction on that last one would be simple.

But because of the First Amendment, it’s not.

Though the First Amendment says, “Congress shall make no law” suppressing free speech, the Supreme Court has said in a series of rulings that there are some types of speech that can be punished because they just aren’t worth the trouble they cause.

For instance, you probably couldn’t cry “First Amendment” after you falsely yelled “fire” in a crowded theater and caused a panic, Justice Oliver Wendell Holmes famously wrote in 1919.

But words have to be pretty extreme and obnoxious to fall outside free-speech protections.

What’s said must amount to “fighting words” or incite “imminent lawless action” or convey “true threats.”

But the outer boundaries seem to shift with the times.

In 1942, you couldn’t call someone “damned racketeer” and “damned Fascist” on a public street because, the Supreme Court said, that was likely to provoke retaliation and a breach of the peace.

But in 1969, the court said it wasn’t punishable for a Ku Klux Klan leader, at a rally with burning cross, to say if federal officials continued “to suppress the white, Caucasian race, it’s possible that there might have to be some revengeance taken.”

So where do shock jock/blogger Hal Turner’s words fall?

Turner spews hate that his lawyers describe as political hyperbole, according to accounts of his trial.

After Judges Richard Posner, Frank Easterbrook and William Bauer ruled that a lower court properly dismissed a challenge to handgun bans in Chicago and Oak Park, Turner wrote online, “These judges must die. Their blood will replenish the tree of liberty.”

He also referred to the 2005 killings of U.S. District Judge Joan Lefkow’s husband and mother at their home. Authorities initially suspected that white supremacist Matthew Hale might be behind the crime because he previously tried to have Lefkow killed. It turned out that the killer was a man upset that the judge had dismissed his medical malpractice suit.

“Apparently, the 7th U.S. Circuit didn’t get the hint after those killings. It appears another lesson is needed,” Turner is alleged to have written.

He also posted the appellate judges’ pictures, phone numbers, work addresses and a map of the federal building where they work.

During his trial (covered extensively by the Record at northjersey.com), his lawyers argued that he was an FBI informant who was coached to egg on extremist groups. But an agent testified that the FBI never told Turner to use violent threats, the Record reported. (A retrial is set for March.)

Another extremist talker is on trial in Roanoke, Va.

Neo-Nazi William A. White is accused of going after seven people, ranging from a bank employee in Kansas City to Miami Herald columnist Leonard Pitts Jr.

According to testimony chronicled by the Roanoke Times ( www.roanoke.com), White had a credit card dispute with Citibank, so he found an employee’s home address, phone number and husband’s name and e-mailed them to her, along with a link to information about the Lefkow killings, saying that “making people upset is what did in Joan Lefkow.”

He also posted Pitts’ home contact information online and sent Pitts a slur-filled e-mail telling him to expect a visit from The Aryan Brotherhood, the Times reported. When a Herald editor asked White to remove the Web posting with Pitts’ contact information, White reportedly replied, “Frankly, if some loony took the information and killed him, I wouldn’t shed a tear. That also goes for your whole newsroom.”

On Wednesday, a University of Delaware employee testified that White complained about a diversity awareness program with this message for an administrator: “Just tell her that people who think the way she thinks, we hunt down and shoot.”

The First Amendment can tolerate a lot of speech that some of us personally cannot. But at some point hating turns to instigating. The line shouldn’t have to be drawn in someone’s blood. That can’t be what the founders had in mind.