Los Angeles is one of the bluest metro areas in the country, but the mayor’s race this year increasingly feels like Rick Caruso’s to lose. The billionaire real estate developer is running what amounts to a law and order campaign, in a city grappling with a rise in violent crime and an intractable homelessness problem, far and away the top concerns for Angelenos of all races and income levels. Since joining the race in February, Caruso has spent more than $30 million of his own money on advertising promising to “clean up L.A.,” a message that has vaulted him to the top of the field, even according to internal polls released by his rivals.