Rep. Seth Moulton, an Iraq War veteran and leading rebel against House Democratic leadership, announced Monday he's mounting a campaign for president, joining a crowd of 18 other Democrats who want to challenge President Donald Trump in 2020.

"I'm running because we have to beat Donald Trump," Moulton said a video on Twitter. "And I want us to beat Donald Trump because I love this country."

Moulton's first task will be to distinguish himself from a collection of candidates with wider name recognition and established political organizations who have already been raising money, collecting endorsements and hiring staff in early primary and caucus states. Still more candidates are expected to join the race in the coming weeks, including former Vice President Joe Biden.