David Frum zeroes in on the sort of rhetoric that's worth worrying about:
The problem is not military metaphors. It's not Glenn Beck joking about poisoning Nancy Pelosi's wine or Paul Krugman hanging Joe Lieberman in effigy at a party. The problem is, rather, the construction of paranoid narratives that might justify violence to a violent-minded person. When scruffy protesters drew swastikas on photographs of President George W. Bush, that was obnoxious. It was not likely to incite anyone. But when eminent persons argued on the public airwaves that the United States had been lied into a frustrating war in Iraq by a cabal of Jewish conspirators? That’s a very different matter.
Likewise, it's grossly ill mannered for a member of the House to shout "You lie!" at a president during a State of the Union address. Yet the republic staggered on somehow. What does do damage to the fabric of democracy is the charge made by prominent conservative broadcasters that the president is deliberately wrecking the U.S. economy to advance his scheme to overthrow the constitution and transform the nation into a Marxist or Leninist or even Maoist tyranny.
Or a Kenyan anti-colonialist's paradise.