New York has just elected a mayor whose politics make Ken Livingstone look like Norman Tebbit and it is the first time in twenty years that this heavily Democratic city has elected a Democratic mayor.
The main reason for this is that New York used to have a horrendous crime problem until Rudolph Guliani took office and reduced it massively and Bloomberg continued the process. Under the two Republicans (very nominally so in Bloomberg's case) the Big Apple became a liveable city once more.
Washington has undergone a similar transition lately, with crime falling considerably. It used to be one of the USA's most violent cities, ranking alongside Baltimore, Detroit and New Orleans but since 2008 the homicide rate has fallen by half from 31 per 100,000 to 14 per 100000. This is still a very high rate by most standards but it is a massive turnaround for a city that had seen rates over 80 per 100000 in the recent past.
New York rewarded the leaders who slashed the crime rate by re-electing them repeatedly over two decades. Washington has taken a different approach- with the mayor who presided over this unprecedented turnaround being unceremoniously turfed out of office.