Ok I am overestimated the readers ability to research for themseves, but I see catspaw49 did some of that for everybody. The rest is very simple,
Puritanical rigthwing neo-con lunatics have barred millions from voting for being poor, for having moved to a new address and not informing Her Siezersssss new HomeSS about it. Then there are the millions of people rairoaded in states with contracted out detainment social education services ( IOW rent a jail dot inc ). They create crime on the side to keep their business running. Try Oklahoma Mississippi and any other poor state for the same kind of rubbish. Next all legal aliens are barred no matter how long they have lived in the USA. Last but not least the recent influx of Latinos who BTW have enormous political clout!

So instead of leaning on the troll button some of yall should be out there doing the folkie thing and making it hell for the conslobs who are such bunch of hypocrits!

The census does ask about registration BUT it does not report those who cannot vote, that figure is estimated from those who do not respond, so yes 33% is an accurate if low estimate of the number.