“As President I have an obligation to end CORRUPTION, even if that means requesting the help of a foreign country or countries. It is done all the time,” Trump wrote Friday morning on Twitter. “This has NOTHING to do with politics or a political campaign against the Bidens. This does have to do with their corruption!”

Trump previously asserted in a tweet Thursday night that he has “an absolute right, perhaps even a duty” as president “to investigate, or have investigated, CORRUPTION, and that would include asking, or suggesting, other Countries to help us out!”

House Intelligence Chairman Adam Schiff (D-Calif.) responded to that post Friday, imploring his GOP colleagues to break with the president.

“It comes down to this. We’ve cut through the denials. The deflections. The nonsense,” he tweeted. “Donald Trump believes he can pressure a foreign nation to help him politically. It’s his ‘right.’ Every Republican in Congress has to decide: Is he right?”

Among Republicans in Congress, Sen. Mitt Romney (R-Utah) on Friday delivered the most forceful rebuke of Trump, calling the president's appeal to the Chinese and Ukrainian governments “wrong and appalling.”

“When the only American citizen President Trump singles out for China’s investigation is his political opponent in the midst of the Democratic nomination process, it strains credulity to suggest that it is anything other than politically motivated,” Romney tweeted.

The president’s latest rationale for his behavior came as Washington awoke Friday to news of damaging text messages exchanged in recent months among top American diplomats. Those communications — which Kurt Volker, the former special envoy to Ukraine, provided Thursday to congressional Democrats — detailed efforts by the administration to pressure Zelensky to investigate the Bidens and alleged meddling by the Eastern European nation in the 2016 election.

The texts are certain to open a new front in the impeachment drive by Democratic lawmakers, who say the explosive messages offer clear evidence that Trump made U.S. military aid and a White House visit contingent upon Zelensky's approval of the investigations. The president's Republican defenders on Capitol Hill have so far argued that he proposed no such quid pro quo during his conversation over the summer with his foreign counterpart.

Sen. Chris Murphy (D-Conn.) warned Friday that the revelation of the texts marked an “important moment for our democracy.”

“We now know that Trump was using access to the White House to get a foreign government to help destroy his political rival,” he tweeted. "There was an explicit quid pro quo: open an investigation into my rival, and I will invite you to the White House.”

Murphy wrote in another post that while “it’s never been necessary to show an explicit quid pro quo,” the texts also “make it pretty clear the aid was being withheld until Zelensky chose to investigate.”

House Democratic Caucus Chairman Hakeem Jeffries (D-N.Y.) also tore into the president after the new evidence emerged. “Trump withheld $391 million in security aid for no reason. He then pressured the Ukrainian President to target an American citizen for political gain. How do you describe this extraordinary betrayal of America’s national security?” he tweeted, adding, “ABUSE OF POWER.”