The topic of assassination has been unthinkable during the early months of Barack Obama’s presidency. But in light of the right-wing rage on display at health-care town halls this month — combined with new information that the president is receiving around 900 threats per month, a 400 percent increase over threats against George Bush — the topic has unfortunately become a lot less unthinkable.

In an op-ed in the Washington Post today, David Broder suggests Republicans are “playing with fire” by fanning the flames with talk of incipient socialism and by promoting lies about reforms, including the lie that will not die, that Obama plans to set up “death panels” with the power to euthanize seniors and the handicapped.

Broder means GOP leaders are playing with fire politically, of course. Their objective in ginning up the hysteria is to drive a wedge between Blue Dog Dems and the right-leaning independents whose votes they must have to stay in office. Broder warns the GOP leaders that the party could face a backlash from normal Americans who find the rage of the town-hall disrupters off-putting and who see through the lies about reforms.

Broder — the capitol’s leading regurgitator of conventional wisdom — is not ready yet to accuse his GOP buddies (and key sources) of fanning the flames of violence. But a new metric about the threat level faced by this president should give pause even to David Broder, the ultimate promoter of the status quo.

According to a new book, “In the President’s Secret Service,” by Richard Kessler, Pres. Obama receives as many as 30 death threats a day. That’s as much as 900 threats a month — roughly 7,000 threats since the president was inaugurated.

Given statistical probability — combined with the fact that the right-wing fringe has produced Timothy McVeigh, Olympics bomber Eric Rudolph, Scott Roeder, the murderer of Dr. George Tiller, and other killers in recent years — it is a dead cinch that one of these lunatics will take the threat to the next level and launch a violent attack against the president someday soon.

Over the top, you say?

Consider the case of William Kostric, the New Hampshire man who showed up outside Pres. Obama’s town hall on health-care reform in New Hampshire this week with a loaded handgun strapped to his leg and carrying a sign that read, “It Is Time to Water the Tree of Liberty.” (When asked later if the gun was loaded, Kostric said, “Who’d be silly enough to carry an unloaded firearm?”)

The full quote from Jefferson is, “The tree of liberty must be refreshed from time to time with the blood of patriots and tyrants.” You’ll notice that the wording of Kostric’s sign left him with Eddie Haskell-esque deniability — “I didn’t say Obama was a tyrant” — because threatening the president is illegal.

But was Kostric — a libertarian Birther — there to threaten the president’s life? No. No more than Madame DeFarge called for the deaths of her enemies as she tending her knitting. On the other hand, the simplest decoding of Kostric’s sign is, “It Is Time to Spill the Blood of the Tyrant Obama.” But if he’d said that, he would have been arrested.

At the same rally, Richard Terry Young was arrested for sneaking past security agents into a restricted zone. A search of a bag in his car produced a .380 Kel Tec semi-automatic with a round in its chamber.

It was Sarah Palin, in her role as the GOP vice presidential nominee, who first captured the zeitgeist of white conservatives’ agitation over the imminent rise of a black man to leader of the free world. “I am just so fearful that this is not a man who sees America the way that you and I see America,” she said at a rally last year. As the campaign wore on, she hammered at the idea that Obama was different, not one of us — the sort of interloper who disdained America so much that he thought nothing of palling around with a terrorist. Finally, someone in the crowd, speaking for many, yelled, “Kill him!”

Violence-prone wingnuts are particularly susceptible to suggestion. After the right-wing terrorist Jim Adkisson opened fire in a liberal church in Knoxville in July 2008, killing two and wounding seven, a search of his lair uncovered a small library of right-wing propaganda, including “The O’Reilly Factor,” by Bill O’Reilly, Sean Hannity’s book,”Liberalism is a Mental Health Disorder,” and Michael Savage’s “Let Freedom Ring.” Adkisson told a local reporter he’d targeted the Unitarian church because he believed that all liberals should be killed because they were ruining the country.

In the past few months, the propagandists have ratcheted up their rhetoric. Rush Limbaugh has compared Obama to Hitler and Democrats to Nazis. CNN’s Glenn Beck has called Obama a racist who hates white people. While Beltway pundits and media types find this sort of talk to be silly and juvenile, it is dog-whistle messaging directed at a certain element in the far right base: “Democracy has failed you. It is time to water the tree of liberty.”

Despite their own heated rhetoric, Republican leaders will deny responsibility for the threat of violence charging the atmosphere. While it’s true they didn’t conjure it up, they and they alone have the power to dispel it. They won’t, and that is risky — far riskier than the trap Broder fears they have laid for themselves.

If Kostric’s call to arms is answered and there is bloodshed, especially if there were to be an attack on the president, Republican leaders will be held accountable — not from liberals alone but from all decent Americans, whose grief and anger would make the outrage over 9/11 pale in comparison.