U.S. Representative Eric Swalwell on Monday became the first major candidate to drop out of the Democratic presidential race, ending a long-shot bid fueled in part by his efforts to investigate Republican President Donald Trump.

"I thank my supporters & friends, my staff, & my family for making this journey possible," 38-year-old Swalwell said on Twitter, adding that he planned to run for re-election to Congress in his California district.

He said on Monday he was not prepared to make an endorsement in the crowded Democratic contest for the right to face Trump in the November 2020 presidential election.

Swalwell was one of the more aggressive candidates on the Democratic debate stage last month, challenging former vice president Joe Biden, 76, to "pass the torch" to a younger generation.

But the approach did little to improve his standing in opinion polls among the more than 20 Democrats seeking the party's nomination. He was in jeopardy of falling short of the qualification requirements for the next round of debates later this month.

Swalwell has raised his profile in recent years by becoming a staple on cable television news, especially to talk about investigations of the Trump administration. But he consistently trailed in 2020 presidential polls.

(Cover: U.S. Representative Eric Swalwell speaks during the second night of the first Democratic presidential candidates debate in Miami, Florida, U.S., June 27, 2019. /Reuters Photo）