When Mitt Romney cast a vote for Sen. Paul Tsongas (D-MA) in 1992, he formally enrolled in the Democratic Party, BuzzFeed reports.
"Romney registered to vote in 1976 as what Massachusetts authorities now call an 'unenrolled' voter -- a member of neither party. Under state law, primaries are open, and unenrolled citizens may participate in either primary. But under the law as it stood in 1992 -- it was changed in 2004 -- 'essentially enrolled unenrolled voters (commonly referred to as independent) into the political party based on the ballot they chose at the presidential primary... After voting, a voter would have had to 'unenroll' by completing additional paperwork to go back to their 'independent' status.'"