Washington (CNN) 2020 Democratic presidential candidate Beto O'Rourke said Saturday that the "single best thing" to unify the country would be for President Donald Trump to resign for his actions related to Ukraine.

"The best possible path, especially if you're concerned about a country that's never been more divided, perhaps more highly polarized every day, is for this President to resign, allow this country to heal and ensure that we come back together with the greatest, most ambitious agenda we've ever faced, none of it possible while he remains in power," O'Rourke said at the Texas Tribune Festival in Austin.

House Democrats launched a formal impeachment inquiry this week into Trump related to a whistleblower's allegations that he pressured Ukraine's President to investigate former Vice President Joe Biden, another 2020 contender.

O'Rourke said Saturday that "beyond the shadow of a doubt, we now know that the President must be impeached."

He applauded House Speaker Nancy Pelosi for moving ahead with an impeachment inquiry and said he's "cautiously optimistic about the path that we're on now."

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