President Trump suggested Sunday that he mentioned former vice president Joe Biden and his son Hunter in a phone call with the leader of Ukraine, as Democrats ramp up their calls for accountability amid swirling questions about whether Trump sought to use his influence to seek re-election help from a foreign country.

In an exchange with reporters outside the White House before departing for events in Texas and Ohio, Trump was asked about his July 25 conversation with Ukrainian President Volodymyr Zelensky. The Washington Post reported last week that Trump pressured Zelensky to investigate a company with ties to Hunter Biden, and the call between Trump and Zelensky is the subject of an extraordinary whistleblower complaint.

“The conversation I had was largely congratulatory, was largely corruption, all of the corruption taking place, was largely the fact that we don’t want our people, like Vice President Biden and his son, creating to the corruption already in the Ukraine,” Trump told reporters. “And Ukraine, Ukraine’s got a lot of problems.”

Trump has denied that he has done anything untoward in his conversations with world leaders and had previously declined to say whether he spoke with Zelensky about Biden, who is leading in polls for the 2020 Democratic presidential nomination.

Later Sunday afternoon, in an exchange with reporters in Houston, Trump confirmed that he will meet with Zelensky this week at the United Nations General Assembly in New York. He also said his administration will “make a determination” about releasing a transcript of the call, which he maintained was “absolutely perfect.”

The developments have ratcheted up pressure on congressional Democrats to pursue impeachment proceedings against Trump. House Speaker Nancy Pelosi, D-Calif., who thus far has rebuffed the impeachment calls from rank-and-file members of her party, signaled a shift in her position in a letter to all House members on Sunday.

The Trump administration, she said, “is endangering our national security” by blocking the release of the whistleblower’s full complaint.

“If the administration persists in blocking this whistleblower from disclosing to Congress a serious possible breach of constitutional duties by the president, they will be entering a grave new chapter of lawlessness which will take us into a whole new stage of investigation,” Pelosi said in the letter.

News of Trump’s call with Zelensky came to light after an intelligence official whistleblower shared with the intelligence agency’s inspector general that the official had heard Trump make a promise to a foreign leader that wasn’t appropriate.

Subsequent reporting has found that the call was with Ukraine and related to Trump’s desire to get dirt on a political opponent. Congress has not been provided a copy of the actual complaint filed by the whistleblower.

Trump’s apparent confirmation that he mentioned Biden on the call with Zelensky came as his allies scrambled to deny that he did so.

Sen. John Cornyn, R-Texas, said there is “no direct evidence” that Trump asked Zelensky to investigate Biden or his family, saying the allegation is “based on hearsay reports.”

“I just frankly can’t imagine why people have lost their minds so much over these daily reports of one thing or another that seem to consume everybody’s attention in the news coverage,” Cornyn told reporters ahead of Trump’s event in Houston.

On NBC News’ “Meet the Press,” Treasury Secretary Steven Mnuchin repeatedly declined to say whether it was appropriate for the president to ask a foreign leader to investigate a political rival and suggested that Trump did not pressure Zelensky.

“You’re speculating that the president pressured. I don’t have any reason to believe that the president pressured … in any way,” Mnuchin said.

Rudy Giuliani, Trump’s personal attorney, said in a phone call Sunday morning with The Washington Post that he has been “working for months for this moment” and this week will “keep pushing and pushing” to highlight the Biden family’s finances. He alluded to new materials he may cite this week, but declined to offer specifics.

When asked whether Trump has given Giuliani’s efforts his blessing, Giuliani said, “I don’t do anything that involves my client without speaking with my client.”

On Saturday, Biden swung back at Trump and challenged the president to release a transcript of his phone call with Zelensky.

“Trump’s doing this because he knows I will beat him like a drum and is using the abuse of power and every element of the presidency to try and smear,” Biden told reporters at the Polk County, Iowa, Steak Fry.

Trump also on Sunday took aim at Biden for saying that he never spoke with his son about his overseas business dealings, telling reporters, “I mean, give me a break.”

“This is a very dishonest thing that Joe Biden did,” Trump said, repeating his attacks on the Biden’s family business dealings. “And then he said he never spoke to his son. Does anybody believe that one?”

Trump has repeatedly claimed that he did not speak to his son, Donald Trump Jr., in advance about a June 2016 Trump Tower meeting at which Russians had offered to provide dirt on Democratic presidential nominee Hillary Clinton.

In addition to Pelosi, other Democrats on Sunday inched closer to calling for impeachment proceedings against Trump.

House Intelligence Committee Chairman Adam Schiff, D-Calif., said on CNN’s “State of the Union” that while he has been reluctant to pursue impeachment, it may be the “only remedy” to the “evil” represented by Trump’s alleged effort to pressure Ukraine into providing dirt on Biden by threatening to withhold U.S. military aid.

Former secretary of state John Kerry argued that if Trump indeed pressured Zelensky on the call, Republicans are “inadvertently supporting a coverup” by not calling for a transcript to be released.

“Let everybody see what the president said,” Kerry said on CBS News’ “Face the Nation.” “And if he leveraged American foreign policy and foreign aid to get a president of another country to be the opposition research arm of his campaign, that is a fundamental, profound and deeply disturbing abuse of power.”

Trump administration officials and Republican lawmakers defended the president and sought to place the focus on Biden in appearances on the Sunday morning news shows.

In his “Meet the Press” interview, Mnuchin argued that rather than focusing on “confidential discussions” between two world leaders, “I really think that the real issue here is not what the president said but what indeed did Biden’s son do.”

Mnuchin struggled, however, when asked during a separate interview on CNN’s “State of the Union” about his claim that the Biden family’s business dealings in Ukraine were “inappropriate.”

“I don’t understand,” host Jake Tapper said. “So it is OK for Donald Trump Jr. and Eric Trump to do business all over the world – it’s OK for Ivanka Trump to have copyrights approved all over the world while President Trump is president – but while Vice President Joe Biden was vice president, his son shouldn’t have been able to do business dealings?”

Mnuchin responded that there was a “significant difference” between the Bidens’ dealings and the “potential business dealings that the Trump Organization has had, which predated his presidency.”

Other officials were pressed about the role that Giuliani has played. In meetings overseas with Ukrainian officials, Trump’s personal attorney has pushed for reopening an investigation of the gas company that had hired Hunter Biden to serve as a board member and adviser while his father was U.S. vice president.

Secretary of State Mike Pompeo was asked during an interview on “Face the Nation” whether he believes it’s appropriate for Giuliani to be “inserting himself into foreign affairs like this.”

Pompeo responded that “if there was election interference that took place by the vice president, I think the American people deserve to know.”

He declined to say whether he has personally asked Zelensky to open an investigation or whether the U.S. Embassy in Ukraine is involved in supporting Giuliani’s efforts.

In an appearance on “Fox News Sunday,” Giuliani repeatedly took aim at the former vice president and his family, at one point referencing Hunter Biden’s struggle with addiction and mental health.

“The kid, unfortunately, is a drug addict,” Giuliani said.

Joe Biden has spoken openly about his son’s struggles, including in a CNN interview that aired days after the New Yorker published a lengthy story about Hunter Biden in July.

Sen. Lindsey Graham, R-S.C., called for the Justice Department to play a role in the matter, arguing that it should “do for the Biden-Ukraine connection” what was done for the Trump-Russia connection, in a reference to former special counsel Robert S. Mueller III’s Russia probe.

“What role did the Bidens play? … There’s enough smoke here,” Graham said on Fox News Channel’s “Sunday Morning Futures.”

The Washington Post’s Philip Rucker, Robert Costa, Colby Itkowitz, Matt Zapotosky, Jonathan O’Connell and Rachael Bade contributed to this report.