The reposts and expressions of shock from public figures followed quickly after a user on the social platform X who uses a pseudonym claimed that a government website had revealed “skyrocketing” rates of voters registering without a photo ID in three states this year — two of them crucial to the presidential contest. “Extremely concerning,” X owner Elon Musk replied twice to the post this past week. “Are migrants registering to vote using SSN?” Georgia Rep. Marjorie Taylor Greene, an ally of former President Donald Trump, asked on Instagram, using the acronym for Social Security number. Trump himself posted to...