As regards the fellow who threatened Eric Cantor, according to TPM he has a problem with lots of people:
It wouldn't make any difference if he had given money to Sarah Palin. The right wingers were able to sell the idea that the Islamic fanatics who shoot women like dogs, hang gay people and want to take the world back to the 11th century are big allies of the feminazi, gay marrying liberals. This does not require any intellectual coherence. All they need to know is that this particular nutcase threatened a Republican lawmaker to prove that it's the liberals who are threatening violence and the conservatives who are the victims. And this naturally leads to the conclusion that the conservatives must "fight fire with fire," arm up and defend themselves.
According to the federal complaint against him, Norman Leboon of Philadelphia has admitted making some 2,000 videos that contained threats. A sampling of his "work" reveals rambling incoherent videos that mix pseudo-religious incantations with random warnings and threats. In one video he addresses President Obama, Vice President Biden, Nancy Pelosi and Harry Reid by name and says, "Your punishment is coming, the swine, it will be severe, and you will beg for mercy to your god, it will be severe, you will know god's swine, god has warned you." (Some conservatives are already chortling over the fact that Leboon contributed to Obama's 2008 campaign, though it's not clear what that's supposed to signify.)
It's not an original rationale, god knows. It's been used to justify wars since time began --- even as recently as 2003. But considering that Newt Gingrich is going around saying that Obama is "the greatest threat to the American way of life since the 1850s," it's something worth thinking about.