What concrete steps are being taken not only to detect invalid registrations but also fraud once an invalid voter has submitted a ballot? I know this probably differs state by state though am interested to hear what is being done to minimize this problem.
You need to keep asking that question.
Ask: (1) The Republican Party, (2) the prosecuting attorneys' orifices, (3) the law enforcement agencies.
They need to get these questions from many, many, many people EVERY TIME there is a substantiable accusation of fraud. Enough "encouragement" of that sort, and they'll realize that there is some agitation out there about this.
There are various things they can do... whether they're doing them all, or not, is another question. I've been posting repeatedly to these threads asking what exactly Demonrats would have to do to commit actual voting fraud - not just registration fraud, but *actual vote fraud*, because that's what we have to care about. Just registering 184 people at every Demonrat local office won't cut it - they have to *vote* those people, and that requires a coordinated campaign of fraud and deception which *can* be detected by effective law enforcement.
Voter rolls can be scanned automatically for large numbers of people registered at one address. If voter registration cards are required, they will have to be mailed to an address.
Video cameras can be put in place at the polling locations. The Demonrats ought to be only too happy to do that, so that they can catch the (nonexistent) Evil Republicans scaring wimmen-n-minorities away from the polls, right? Problem for them is that it will also capture on camera anyone who tries to vote twice - and, most importantly, they'll *know* they're on camera.
Here in Oregon, where we vote by mail, elections orificials have your signature on file from your voter registration and it pops up on their screen (yes, they're digitizing your signature - Think you're safe from someone raiding a Gummint database and using your signature to commit fraud?) so they can compare it with your signature on the registration you sent in. We will have monitors watching the elections officials for irregular behavior, such as not rejecting any at all or rejecting too many.
I could carry on for page after page, but the bottom line is (1) you can't sit around and wait for someone else to put the Gubmint (and the Republican Party, FTM) on the spot to do its job - you have to start asking those questions of them yourself, (2) you can VOLUNTEER for the Republican election monitoring teams.