From what I can find Maryland does not verify US citizenship to register to vote, they accept a drivers license # or SS ## for registration. And a legal resident with a Green Card can have those.
The application requires them to swear that they are a US citizen under law on the application, that’s it.
So non-citizens can easily vote here illegally if they want to.
It suddenly occurs to me that's why the Clintons implemented "motor voter" duh for me....