Yes you have to be registered, but that requires no verification of citizenship and states are only allowed to verify citizenship theoretically since 2016, but they don't have to. Which is my whole arguement.
The twitter posters were cited because your linked wapo article claims no significant voter fraud is happening based on anecdotal evidence of lazily searched news articles of voter fraud, it is only fitting to bring up annecdotal evidence of twitter users showing that voter fraud by illegal immigrants is indeed happening.
The only reason democrats are supposedly against voter id laws is that they believe minorities are too stupid to register to vote (seriously, google what Debbie Wassermann Schulz says about it), this reasoning is completely and utterly racist and frankly disgusting on a lot of levels.
Sorry democrats, other countries with voter id laws have minorities too and they can and do in fact vote. Again, I am not claiming that Trumps numbers are accurate, but you can't even remotely prove or disprove them because you don't have voter id laws because supposedly american minorities are too stupid to fill out government forms if democrats are to be believed (cough, racist, cough).