2020 democratic presidential primary

Brown is the latest to pass on the 2020 race. He was re-elected last year, promising to "do everything he can" to elect a Democratic president and Senate in 2020.

Gillibrand joins a growing field of Democratic candidates, telling TV host Stephen Colbert on Tuesday that she is launching an exploratory committee and explaining why she has decided to run.

His announcement came Saturday in Texas, after weeks of hinting he was ready to join the 2020 Democratic primary field. "I've always believed with big dreams and hard work anything is possible."