A Must Read: The reckless Right courts violence by David Frum in The Week Magazine.

Hysterical talk from TV and radio hosts may be a cynical marketing exercise. But it's getting too dangerous to ignore.

A man bearing a sidearm appears outside President Obama's Aug. 11 town hall meeting in Portsmouth, N.H., under a sign proclaiming, "It is time to water the tree of liberty."

That phrase of course references a famous statement of Thomas Jefferson's, from a 1787 letter: "The tree of liberty must be refreshed from time to time with the blood of patriots & tyrants."

Earlier that same day, another man is arrested inside the school building in which the president will speak. Police found a loaded handgun in his parked car.

At an event held by Rep. Gabrielle Giffords in Arizona last week, police were called after one attendee dropped a gun.

Nobody has been hurt so far. We can all hope that nobody will be. But firearms and politics never mix well. They mix especially badly with a third ingredient: the increasingly angry tone of incitement being heard from right-of-center broadcasters.

The Nazi comparisons from Rush Limbaugh; broadcaster Mark Levin asserting that President Obama is "literally at war with the American people"; former vice presidential candidate Sarah Palin claiming that the president was planning "death panels" to extirpate the aged and disabled; the charges that the president is a fascist, a socialist, a Marxist, an illegitimate Kenyan fraud, that he "harbors a deep resentment of America," that he feels a "deep-seated hatred of white people," that his government is preparing concentration camps, that it is operating snitch lines, that it is planning to wipe away American liberties": All this hysterical and provocative talk invites, incites, and prepares a prefabricated justification for violence.

And indeed some conservative broadcasters are lovingly anticipating just such an outcome.

Here's Fox News' Glenn Beck clucking sympathetically that white males are being driven into murderous rage by "political correctness."

Here again is Beck chuckling as he play-acts the poisoning of Nancy Pelosi.

Just yesterday, the radio host Sean Hannity openly contemplated violence—and primly tut-tutted that if it occurs, the president will have only himself to blame.

Hyperbolic accusation and fantasy murder may well serve a talk-radio industry facing a collapse in advertising revenues—down 30–40 percent over the past two years, reports NewMajority.com's Tim Mak.

As revenues dwindle, hosts feel compelled to intensify the talk-radio experience, hoping to win larger audience share with more extreme talk. It's like the early days of the pornography industry: At first a naked woman is thrilling enough, but soon a jaded audience is demanding more and more, wilder and wilder.

For the radio hosts, it's all mostly a cynical marketing exercise. But the audience? Not all of them know better.

In April, the Department of Homeland Security released a report warning of the danger of right-wing political violence in the United States, and mainstream conservatives erupted in offense.

National Review's Jonah Goldberg wrote: My real objection to this report is that its source material amounts to "everybody knows." Everybody knows the right is full of whack-jobs, hatemongers, and killers, and if we don't remain vigilant, bad things will happen.

Michelle Malkin asked in her syndicated column: What and who exactly are President Obama's Homeland Security officials afraid of these days? If you are a member of an active conservative group that opposes abortion, favors strict immigration enforcement, lobbies to protect Second Amendment rights, protests big government, advocates federalism or represents veterans who believe in any of the above, the answer is: You.

Newt Gingrich tweeted: "The person who drafted the outrageous homeland security memo smearing veterans and conservatives should be fired."

I don't think the former speaker could tweet such a thing today in good conscience. The person who drafted that homeland security memo has gained very good reason to be worried. The guns are coming out. The risks are real.

It's not enough for conservatives to repudiate violence, as some are belatedly beginning to do. We have to tone down the militant and accusatory rhetoric. If Barack Obama really were a fascist, really were a Nazi, really did plan death panels to kill the old and infirm, really did contemplate overthrowing the American constitutional republic—if he were those things, somebody should shoot him.

But he is not. He is an ambitious, liberal president who is spending too much money and emitting too much debt. His health-care ideas are too ambitious and his climate plans are too interventionist. The president can be met and bested on the field of reason—but only by people who are themselves reasonable.