Ross Douhat of The New York Times states it clearly. "if overheated rhetoric and martial imagery really led inexorably to murder, then both parties would belong in the dock." But he's wrong. It's not both sides equally. No one is threatening right-wing leaders with violence or "second amendment remedies" as the Republican nominee for Nevada Senate did.
It's the right-wingers in America who are threatening violence, and that is exactly what they did when they sent individuals carrying firearms to Democratic political rallies. Firearms are a symbol that violence is being threatened. They use the rhetoric that guns are for defense, but that's only true for people working for the government. Anyone else who carries a gun does so because he he afraid, angry at someone else, or insane. He displays it to threaten violence and to intimidate those he is threatening.
Why do I exempt people with the government? Because the first function of a government is always to maintain social stability and the government must maintain a monopoly on the legitimate right to use violence to maintain social stability.
Notice that social stability was NOT maintained in the parking lot of Safeway. There were people there with legal concealed weapons, but the shooting started and was over in less than 15 seconds. Untrained carriers of so-called defensive firearms got to show up in time to see the blood and bodies on the ground. The violence was ended by unarmed civilians before the gun-carriers even realized there was a problem.
The only reason anyone other than a licensed peace officer carries a firearm in a crowd is as a symbolic threat to perform violence ("I'm a bad-ass! Fear me!" or "Better cater to my whims! "I'm armed!" or "You can't threaten me! I'm armed and dangerous!") or in preparation of a terrorist action. The weapon is always a symbol of violence and intimidation.
It is the right-wing that does the threatening of violence because they are the ones most likely to practice it on their political opponents. There is no equivalence on the left.