Trump Said to Have Frozen Aid to Ukraine Before Call With Its Leader

Other, more veteran lawmakers issued similar statements.

Veteran Democrats close to Ms. Pelosi, who has stubbornly resisted impeachment, joined the chorus as well. “An impeachment inquiry may be the only recourse Congress has if the president is enlisting foreign assistance in the 2020 election,” said Representative Rosa DeLauro of Connecticut. “Congress must meet this pivotal moment in our nation’s history with decisive action.”

There were also indications of more movement to come. Other moderate freshmen who have shied away from impeachment spent the day furiously calling one another in efforts to calibrate their responses. Several said privately that they were on the brink of supporting an impeachment process, but that they wanted to first see what transpired Thursday.

Privately, some Democrats and their aides were more cautious, fretting that the transcript of the July call would not be as damning as billed. They worried that the anticipation of its disclosure was replicating the dynamic that surrounded the release of the report by Robert S. Mueller III, the former special counsel who investigated Russia’s interference in the 2016 elections, in which Democrats had expected a set of clear-cut revelations that would all but demand Mr. Trump’s impeachment, but ended up instead with a document that did not move public opinion against the president.

Democrats got some backup in the Senate from Republicans, who have generally split over whether Mr. Trump is obliged to share either the transcript or the whistle-blower complaint with Congress.

“I believe the most helpful report would be a transcript of the president’s conversation with President Zelensky,” Senator Mitt Romney of Utah, the 2012 Republican nominee for president, told reporters. “That, I think, would be the most instructive. But I certainly believe that the whistle-blower report should also be available to Congress.”

Speaking on the Senate floor on Monday afternoon, Senator Mitch McConnell, Republican of Kentucky and the majority leader, accused Democrats of trying to exploit a serious issue for political gain. He said he had confidence that the Senate’s intelligence panel, working quietly on a bipartisan basis, would handle it appropriately.

Reporting was contributed by Sheryl Gay Stolberg, Catie Edmondson, Emily Cochrane, Jonathan Martin, Peter Baker and Julian E. Barnes.