The citizens of Washington DC got the right to elect their own mayor in the mid-70s. They proceeded to elect no one but RATS.
After 20 years of RAT rule, Congress had to establish a financial control board to deal with the mess.
The city is back in control, and the people continue to elect RATS. There has still not been a single GOP mayor.
They came close to electing Carol Schwartz at one point (when she faced off against Marion Barry for his final term). Since DC has only had “Mayors” since 1967 and then not since 1871 and earlier (the last 3 Mayors at that point were Republicans). They had a Board of Commissioners from 1874-1967, which had GOP appointees concurrent with similar party Presidential Administrations.