House Democrats on Friday issued their first subpoena in the impeachment investigation of President Trump, demanding documents from Secretary of State Mike Pompeo and scheduling depositions with officials named in that complaint. One of those officials, Kurt Volker, was Mr. Trump's special envoy to Ukraine. He abruptly resigned on Friday.

At a White House reception for Hispanic heritage on Friday night, Mr. Trump found a supportive crowd — a distraction from the impeachment inquiry now ramping up on the other end of Pennsylvania Avenue.

"We have already begun to reach out to witnesses. We're going to be noticing depositions or interviews as soon as next week. We're going to be holding hearings as soon as we can," said Adam Schiff, chairman of the House Intelligence Committee.

Mr. Trump is facing allegations that he pressured the Ukrainian President Volodymyr Zelenksy to investigate former Vice President Joe Biden, a potential 2020 rival, and Biden's son, Hunter in exchange for military aid.

At a campaign event in Las Vegas on Friday, Biden fought back. "After 70 straight polls have shown me beating him, it is not surprising that I've become the object of his attention," Biden said Friday.

The Trump campaign and Republican National Committee on Friday unveiled a $10 million ad targeting Biden and Democratic lawmakers over what it calls an impeachment charade.

"We're supposed to impeach the president based on a hearsay accusation? One pillar of American justice is you get a chance to face your accuser, and I promise you, we're going to find out who the accuser is," Senator Lindsey Graham said Friday.

A portion of the whistleblower complaint focused on the transcript of the Ukraine call being moved to a separate computer system for highly-classified material. A senior administration official confirmed to CBS News that it was filed in that highly-classified system. White House officials cite leaks as one reason for restricting access to those types of documents.