WASHINGTON >> House Democrats, moving quickly to escalate their impeachment inquiry into President Donald Trump, subpoenaed Secretary of State Mike Pompeo on Friday, demanding that he promptly produce a tranche of documents and a slate of witnesses that could shed light on the president’s attempts to pressure Ukraine to help tarnish a leading political rival.

The subpoena and demands for depositions were the first major investigative actions the House has taken since it launched impeachment proceedings this week in light of revelations that Trump pushed President Volodymyr Zelenskiy of Ukraine to investigate Joe Biden, a contender for the 2020 Democratic presidential nomination, possibly using U.S. aid as leverage.

Democrats said more subpoenas — and possibly the scheduling of their first formal impeachment hearing — would come in the next week.

With Congress now in a two-week recess and lawmakers headed home to their districts, Democrats were working on two tracks, meticulously outlining a rapid-fire set of investigative steps while they honed their messaging for what promises to be a divisive and politically charged process.

The House Intelligence Committee told lawmakers to be ready to participate in a Ukraine-related public hearing next week, and it scheduled a private briefing for next Friday with Michael Atkinson, the intelligence community inspector general who first notified Congress of an “urgent” whistleblower complaint related to Trump and Ukraine.

The White House and State Department did not immediately respond to the Democrats’ request. But Trump began his day by attacking Rep. Adam B. Schiff, leader of the Intelligence Committee, and the Republican National Committee was planning a major advertising buy to counter Democratic efforts.

Still, the first potential crack emerged in the so-far nearly united Republican backing for Trump on Friday, when Rep. Mark Amodei of Nevada, a moderate who has broken with the president before, became the first Republican to endorse the inquiry.

The subpoena for documents demands a full transcript of the July call between Trump and Zelenskiy, a list of any State Department officials who listened to or received a readout of the call, and any records created by the department in relation to it. It also seeks any files related to efforts by the president’s personal lawyer, Rudy Giuliani, to push investigations into Biden or other matters involving Ukraine; and it calls for records related to the Trump administration’s decision to temporarily withhold $391 million in security aid from Ukraine.