How the G.O.P. Primary for Mayor Turned 2 Friends Into Bitter Rivals

Two long-shots, Curtis Sliwa, the founder of the Guardian Angels, and Fernando Mateo, a restaurateur, are in a heated fight to be their party’s nominee.

The two Republicans running for mayor of New York City used to be friends. They are both first-time candidates, long shots for the job and tabloid fixtures who perk up when they see a news camera. And now they are at war. At an in-person debate this spring, Fernando Mateo, a restaurateur, threatened his old friend Curtis Sliwa, the founder of the Guardian Angels, for what he said were attacks on his character and warned that he had damaging information about his opponent.