White House hopeful Beto O’Rourke on Saturday called on President Trump Donald John TrumpFederal prosecutor speaks out, says Barr 'has brought shame' on Justice Dept. Former Pence aide: White House staffers discussed Trump refusing to leave office Progressive group buys domain name of Trump's No. 1 Supreme Court pick MORE to resign amid mounting scrutiny over his dealings with Ukraine.

The former Democratic congressman from Texas argued at the 2019 Texas Tribune Festival that "the best possible path" for the country would be 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 added.

O’Rourke and several other Democrats both on the presidential campaign trail and on Capitol Hill have backed a new effort launched by Speaker Nancy Pelosi Nancy PelosiDemocratic senator to party: 'A little message discipline wouldn't kill us' Overnight Health Care: New wave of COVID-19 cases builds in US | Florida to lift all coronavirus restrictions on restaurants, bars | Trump stirs questions with 0 drug coupon plan Overnight Defense: Appeals court revives House lawsuit against military funding for border wall | Dems push for limits on transferring military gear to police | Lawmakers ask for IG probe into Pentagon's use of COVID-19 funds MORE (D-Calif.) to initiate a formal impeachment investigation into Trump.

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Democrats have cited Trump's suggestion to Ukrainian President Volodymyr Zelensky that Ukraine open an investigation into former Vice President Joe Biden Joe BidenFormer Pence aide: White House staffers discussed Trump refusing to leave office Progressive group buys domain name of Trump's No. 1 Supreme Court pick Bloomberg rolls out M ad buy to boost Biden in Florida MORE, the current 2020 Democratic presidential front-runner.

A public memorandum of a July phone call between the two presidents showed that Trump lobbied Zelensky to work with his personal attorney Rudy Giuliani Rudy GiulianiThe Hill's Campaign Report: GOP set to ask SCOTUS to limit mail-in voting CIA found Putin 'probably directing' campaign against Biden: report Democrats fear Russia interference could spoil bid to retake Senate MORE to investigate Biden.

A declassified copy of a whistleblower complaint regarding the call said that a future phone call or meeting between the two presidents “would depend on whether Zelensky showed willingness to ‘play ball,’” and that “multiple White House officials with direct knowledge” of the call were alarmed that Trump appeared to be using his office for his personal political gain.

Trump has denied wrongdoing over the Ukraine conversation and has blasted the whistleblower who filed the complaint against him, questioning whether the individual was a "spy" or "partisan" by raising alarms about his call.

O’Rourke panned Trump earlier this week over the developments, comparing the scandal to Watergate.

“If you looked at the polling on impeachment around [former President] Nixon at this point in the investigation, it wasn’t the most popular thing in the country. Yet with the vantage of hindsight, we know that it was absolutely the right thing to do, and President Nixon did the right thing and resigned before it moved to a trial in the Senate,” O’Rourke said on CNN.

“I’m calling upon those who are close to President Trump now … who right now are complicit in what the president is doing to advise him to do the right thing and to resign from his office,” he added.

O’Rourke shot to national prominence last year with an insurgent Senate bid against Sen. Ted Cruz Rafael (Ted) Edward CruzCrenshaw looms large as Democrats look to flip Texas House seat SCOTUS confirmation in the last month of a close election? Ugly The Hill's Morning Report - Sponsored by Facebook - Trump previews SCOTUS nominee as 'totally brilliant' MORE (R-Texas) that hauled in a record amount of donations, but he has seen his presidential poll numbers plateau near the bottom or middle of most national and statewide surveys.

Despite his lagging polling numbers, O'Rourke on Saturday dismissed speculation that he could head for the exits soon.

“I’m in this thing until the very end,” he said. “I’m in all the way.”