The short-circuit I allude to is the lack of thought put into what happens when an armed assailant is suddenly confronted with an armed defender. While each particular situation has different dynamics, most of the time the standoff will end rather quickly, which usually means less bloodshed.
Three examples of this immediately come to mind.
1. Lantry at Cordite in the Morning links to a story that Doug Powers at Michelle Malkin also mentions, about a church shooting that took place in Aurora (of all places) on April 22, 2012. A newly released felon shot and killed one person before he was killed by an off-duty police officer. Two points are worth making here, besides proving Feinstein wrong. First, the fact that the assailant was a felon with a gun shows that gun control laws are completely useless in stopping criminals bent on committing an armed crime. Second, that the assailant was killed by an off-duty police officer is irrelevant. Any citizen trained to pack could have done the same. The fact that the assailant only killed one person is a tragic victory that more were not killed.
2. Michelle Malkin (different link) also cites another Denver-area story, this one in 2007. On an early December Sunday morning Matthew Murray went on a shooting spree first at a missionary training school and then at a megachurch service until he was shot by Jeanne Assam, described as having law enforcement experience who was volunteering as security for the church's second service. Had Assam not been there to challenge and kill Murray when he refused to stop his attack, many more people would have died.
3. The third example occurred just two weeks ago. Samuel Williams, 71, shot two men who entered an internet cafe in Ocala, Florida, wielding a bat and pointing a gun at customers. The two, both of whom were later caught, were "falling over each other" to get out the door. None of their intended victims was injured. Hmmm.
"The beauty of the Second Amendment is that it will not be needed until they try to take it."
-- Thomas Jefferson