U.S. House Democrats subpoenaed President Donald Trump's lawyer, Rudy Giuliani, for documents on Monday as they ramped up investigations of the president's dealings with Ukraine.

The House Intelligence, Foreign Affairs and Oversight and Reform panels announced the subpoena as they examine Trump's efforts to have Ukraine investigate political rival Joe Biden and his family. Giuliani assisted in that effort.

The committees are investigating the matter, the subject of a now-public whistleblower's complaint, as part of an impeachment inquiry endorsed by House Speaker Nancy Pelosi last week. They are moving rapidly with a goal of finishing the inquiry, and perhaps even voting on articles of impeachment, by year's end.

Both Trump and Giuliani have acknowledged the efforts to influence Ukrainian President Volodymyr Zelensky to investigate Hunter Biden's membership on the board of a Ukrainian gas company at the same time his father was leading the Obama administration's diplomatic dealings with Kiev. There has been no evidence of wrongdoing by either of the Bidens.

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The chairmen of the three committees noted that Giuliani has acknowledged his efforts to pressure Ukrainian officials on national television.

A secret complaint from the whistleblower, whose name is not publicly known, detailed a July phone call between Trump and Zelensky in which Trump urged the probe. It also revealed White House efforts to keep the conversation private.

The subpoena comes as Republican Leader Mitch McConnell said Monday that Senate rules would require him to take up any articles of impeachment against Trump if approved by the House, swatting down talk that that the GOP-controlled chamber could dodge the matter entirely.

"I would have no choice but to take it up," McConnell said on CNBC. But he cautioned, "How long you're on it is a whole different matter."