Democratic members of Congress grappling with the question of impeachment spoke with new urgency on Sunday following reports that President Trump pressured Ukrainian president Volodymyr Zelensky to investigate former Vice President Joe Biden’s son in a July phone call between the two leaders.

The moment arrives amid frustration among some of the candidates running in the 2020 Democratic primary, as well as voters and activists, that the Democratic-led House of Representatives has dragged its feet on holding the president accountable.

In an interview with CNN on Sunday, House Intelligence Committee Chairman Adam Schiff (D-CA) said that impeachment could be the “only remedy,” to the president’s refusal to make public the whistleblower complaint associated with the call and a transcript of his conversation with the Ukrainian president.

“If the President is essentially withholding military aid at the same time that he is trying to browbeat a foreign leader into doing something illicit that is providing dirt on his opponent during a presidential campaign, then that may be the only remedy that is coequal to the evil that conduct represents,” Schiff said, while again stopping short of calling for impeachment proceedings to begin.

Similarly, House Speaker Nancy Pelosi (D-CA) has not and did not join the call for impeachment from a growing percentage of her caucus. But on Sunday, she issued a warning statement about the administration withholding the contents of the whistleblower’s 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 wrote.

Pelosi has faced growing pressure from some Democrats in the House and on the 2020 campaign trail who charge that inaction by the Democratic majority effectively amounts to a seal of approval for the President’s misdeeds.

“At this point, the bigger national scandal isn’t the president’s lawbreaking behavior—it is the Democratic Party’s refusal to impeach him for it,” Rep. Alexandria Ocasio-Cortez (D-NY) tweeted on Saturday night.

Similar sentiments have been expressed by some of the leading candidates for the 2020 Democratic presidential nomination, including Sen. Elizabeth Warren (D-MA) who tweeted on Friday: “ After the Mueller report, Congress had a duty to begin impeachment. By failing to act, Congress is complicit in Trump’s latest attempt to solicit foreign interference to aid him in US elections. Do your constitutional duty and impeach the president.”

On Sunday, Trump confirmed that he did speak with the foreign leader about Biden and defended his actions as appropriate.

“The conversation I had was largely congratulatory, with largely corruption, all of the corruption taking place and 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.

Biden, for his part, has not outright called for impeachment, but during a campaign stop in Iowa over the weekend, he said that the House should investigate the phone call.

“This appears to be an overwhelming abuse of power,” Biden said. “We have never seen anything like this from any president.”