Wayne Lee contributed to this report.
WHITE HOUSE — U.S. President Donald Trump, in his latest remarks explaining his requests to foreign governments to investigate his political opponents, is asserting he has a constitutional duty to fight corruption.
"This is not about politics. This is about corruption. If you look and read our Constitution and many other things, I have an obligation to look at corruption," Trump said to reporters on Friday at the White House.
At the heart of the Democrats' impeachment inquiry in the House of Representatives, which the opposition party controls, is what the intelligence committee's chairman, Adam Schiff, describes as "a damning call in which the President pressured a foreign power to investigate a political rival, harming national security."
Schiff tweeted on Friday that "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?"
In a significant development, Republican Senator Mitt Romney of Utah, tweeted: "By all appearances, the President's brazen and unprecedented appeal to China and to Ukraine to investigate Joe Biden is wrong and appalling."
Romney, himself a former Republican Party nominee for president, is the first senator of his party to directly criticize Trump's actions.
It would take 20 Republicans in the Senate to join all of their Democratic colleagues, plus the two independents who reliably vote with the Democrats to remove the president from office following any impeachment in the House.
Trump said on Friday that while Democrats "unfortunately have the votes" in the House to impeach him, he predicts he will "win" in any subsequent trial in the Republican-led Senate.
Trump again reiterated on Friday that no pressure was exerted during the July 25 call with Ukrainian President Volodmyr Zelenskiy.
The president, however, told reporters on Thursday he would like both Ukraine and China to investigate ties between their countries and the son of former Vice President Joe Biden, a leading Democrat running for president.
Democrats say those statements clearly give them grounds for impeachment and demonstrate Trump is openly abusing the power of his office by asking foreign governments to do his personal political bidding.
"I don't care about Biden's campaign," Trump stressed on Friday. "This is about corruption."
Senior U.S. diplomats urged Zelenskiy to launch an investigation sought by Trump into Biden and his son, Hunter, according to text messages released Thursday by U.S. congressional investigators.
House Democratic investigators released the messages after interviewing former U.S. special envoy to Ukraine Kurt Volker on Thursday for nearly 10 hours.
The texts reveal a discussion between Volker and two other U.S. diplomats about how to handle Trump's requests to investigate Biden and his son.
One exchange shows Volker writing to a top Zelenskiy aide, promising the newly-elected Ukrainian president a visit to the White House in exchange for the probe.
Trump pressed Zelenskiy for an investigation during the phone call that sparked a formal complaint, reportedly by a Central Intelligence Agency officer who had been assigned to the National Security Council. The complaint eventually triggered the House impeachment investigation into Trump.
The president has accused Biden of abusing his power by pressuring Ukraine to back away from a criminal investigation that could have implicated his son.
Trump and his allies have not released any evidence demonstrating the Bidens' were involved in any illegal activity and the former vice president has vociferously defended his reputation in recent days.