The final defeat of Mark Antony and his ally Cleopatra at the Battle of Actium in 31 BC, and the Senate's grant of extraordinary powers to Octavian as Augustus in 27 BC – which effectively made him the first Roman emperor – thus ended the Republic.
@LvChris right now I don’t, but no one has any idea how his second term would go. Does he leave NATO? I suspect more revenge against California, more tax cuts, the wall, end of Roe, and a Court that bends to his will like the Senate. Or, even worse...so, who knows.