From the Australian Election Commission on the matter of voting, " Enrollment on the Commonwealth electoral roll has been compulsory since 1912. Eligible citizens include all Australians citizens who are 18 years of age or over. There are some exceptions, for example in relation to some prisoners, and people of unsound mind (section 93(8) and 96A). Anyone who fails to enroll may be punished on conviction by a fine." 
There are Republicans that have come out forcefully about the President's Conduct. Privately, there are some well known Republicans that question his sanity. And these individuals aren't Democrats! They've said things that weren't said about George W. Bush, George HW Bush, and Ronald Reagan. 
The former DNI Chief, James Clapper, who has been an intelligence official under Republican and Democratic Administrations, said what many intel pros say. They're worried about the man's stability. They're particularly concerned, about the nuclear codes & obession with Kim Jong-un.