No, it's not their fault.
Yes, they made it more likely.
Yes, we have a right to be very scared.
h/t Il Giovine
Nobody in their right mind can blame the Tea Party, or Sarah Palin, or anything else but the disease-addled brain of a sad nutjob for yesterday's shooting. There is nothing eradicable, or even necessarily wrong, about using violent imagery in electoral politics. Preferable as it would be to let such terms remain unused, words like 'crosshairs' or 'target' don't much matter. What matters is if people with power are willing to properly condemn these actions. The Tea Party caucus could have easily said that this guy held perverted version of their beliefs. Instead they claimed that this guy was a 'liberal,' something so obviously false that it would be funny if so many people didn't believe them. Even the insane can properly interpret messages, and in this case the message was unmistakable regardless of how many times denied.
The proper term for what happened is 'incitement to hatred.' A talk-show host who claims that liberalism is 'treasonous' is no different than an imam who claims that all Western Civilization is the devil, or an anti-Abortion activist who claims that abortion should be stopped by any means necessary. The connection between what they say and the actions a few nuts take are not linear, but they are unmistakably sanctioned.
I will never forget the atmosphere in Pikesville in 1995 before Yitzhak Rabin's assassination. We'd read in the Jewish Times about Orthodox Rabbi after Orthodox Rabbi who said that the Peace Process must be stopped and that those who stop it are doing the work of God Him(Her)self. After a few months of this, the unthinkable happened. And so many people rose to the defense of these Rabbis saying that no clergyman ever directly called for the assassination of the Prime Minister (which was not quite true if you read what some Rabbis in Israel were saying). But even if no Rabbi had called for it, the implication of their approval was unmistakable.