"The current administration is making us less prosperous and less secure, the healthcare debacle being the most recent example of their brand of destructive partisanship," Delaney said in a statement announcing his candidacy.
U.S. Representative John Delaney became the first Democrat to formally enter the 2020 presidential campaign to challenge Republican President Donald Trump - more than 1,100 days before the election.
Delaney represents a Maryland district that includes some Washington suburbs.
Traditionally, candidates begin formally announcing their intentions to run for president after the midterm elections, which take place in the middle of the incumbent president's term. The next midterm election will be in November 2018.
Trump formally filed to run for re-election the day after he took office in January.