OBAMA: First, it’s time for Congress to require a universal background check for anyone trying to buy a gun. The law already requires licensed gun dealers to run background checks, and over the last 14 years that’s kept 1.5 million of the wrong people from getting their hands on a gun. (emphasis mine)
First, what are the kinds of things that might cause someone to temporarily fail a background check? Ever try to use a credit card that was refused for no apparent reason? Let's say John K. Smith goes to buy a gun. For some reason a flag shows up in his file because John W. Smith committed a crime last year. So, John K. is denied purchasing a gun...that day, but once they get the records straightened out, Johnny K. gets his gun. His initial denial, however, shows up in that 1.5 million statistic, as if it "kept the wrong person from getting their hands on a gun".
False positives account for some percentage of that number. Far worse is the assumption that when a criminal goes to buy a gun, he A) tries to buy them legally, and B) would accept no for an answer and not try to obtain a gun illegally.
For anyone to say that the "wrong people" are kept from "getting their hands on a gun", is wishful thinking. It might slow them down. That's not necessarily a bad thing, but to assert that "1.5 million of the wrong people" is either naivete of the worst order, regarding black market or stolen firearms, or is an attempt to inflate the mild deterrence of a background check beyond it's true effectiveness (or both).