Former Colorado Gov. John Hickenlooper has ended his longshot bid for the Democratic presidential nomination, and says he's giving "serious thought" to running for the Senate in 2020.

Here's what Hickenlooper says in a video message: "I've heard from so many Coloradans who want me to run for the United States Senate. They remind me how much is at stake for our country. And our state. I intend to give that some serious thought."

Cory Gardner, the Republican incumbent up for re-election next year, is widely considered the GOP's most vulnerable senator because of Colorado's shift to the left.

At least 10 Democrats have already launched campaigns against Gardner.

Hickenlooper ran as a moderate who could unite warring factions of the country. But his genial, quirky style never caught on with a Democratic electorate hungry for a candidate who could take the fight to President Donald Trump.

By the end, Hickenlooper was on his second campaign team and struggling to raise money. He registered at 1% or lower in polls. (AP)