If you are a termed-out politician who will be available for a new job in January, 2021, why not run for president?  That's the situation for two-term New York City Mayor Bill de Blasio who launched his presidential campaign Thursday morning. He becomes the 24th Democrat aspiring to defeat Donald Trump in 2020.

De Blasio made his announcement on Good Morning America. He also released a video titled "Working People First".

De Blasio is the third sitting mayor to join the race. Also running are South Bend Indiana's Pete Buttigieg and Wayne Messam, of Miramar, Florida. No sitting mayor has ever been elected president.