This a BS statistic. If this were true we'd hear about millions of prosecutions of people who unlawfully attempted to buy a firearm. Otherwise ask, why haven't all these people been prosecuted?
The truth is that there were 3 million 'initial rejections' - but nearly all of them were false positives. These are people with similar names (spelled the same, or phonetic similarities). The database basically only checks names. It does not check or validate based on birthdate, drivers license or ID number etc. If your name is similar to that of a prohibited person you get a rejection. Then, you clear up the confusion and buy a gun.
The truth is there were only something like 30,000 people who were prohibited and tried to buy a gun, and only a few dozen of those people were ever prosecuted. People who are prohibited more or less know they are prohibited, and they don't buy their guns from a licensed dealer. There are a few cases where the person didn't know he/she was prohibited, like the 70+ year old man who was convicted of "domestic violence" 40 odd years ago after he got into a brawl with his brother. It was written up as domestic violence before that term became a euphemism for wife-beating, and before the law against domestic violence made you prohibited. He went to buy a gun as a gift for his wife, not realizing he was a prohibited person, and got 2 years in the clink for it.
I should add that a large percentage of the false positives are people of minority status - African Americans and Hispanics - because these groups often have similar sounding or similarly spelled names. The current regime disproportionately discriminates against minorities and it sometimes costs many thousands of dollars to clear up the confusion.
The left doesn’t care much about this kind of systemic abuse, does it?
“background checks” ...... I want somebody to show me where in the Constitution it says that you have to ask permission from the federal govt. to arm yourself. That is what a “background check” is. Asking permission. In fact the 2nd Amendment says exactly the opposite. What part of “Shall not be infringed” do they not understand? Gun control is not about guns. It is about control. The only reason they want a disarmed population, is because they want to do things that they know damned well that a well-armed citizenry would never allow.