WASHINGTON 

US House Republicans escalated their impeachment investigation into President Joe Biden on Wednesday, demanding the White House hand over documents related to the deposition of his son, Hunter. 

James Comer and Jim Jordan, the chairs of the House Oversight and Judiciary Committees, sent a letter to White House Counsel Edward Siskel demanding the White House submit "all documents and communications sent or received by employees of the Executive Office of the President regarding the deposition of Hunter Biden."

The Republican chairmen said they are seeking to determine whether the president worked to "influence, obstruct or impede" their committees' proceedings.

“In light of an official statement from the White House that President Biden was aware in advance that his son, Hunter Biden, would knowingly defy two congressional subpoenas, we are compelled to examine as part of our impeachment inquiry whether the President engaged in a conspiracy to obstruct a proceeding of Congress," they wrote in a joint statement.

The lawmakers referred to comments from White House spokesperson Karine Jean-Pierre during a Dec. 13 press briefing in which she said the president "was certainly familiar with what his son was going to say."

The junior Biden had shown up to Congress that day after being subpoenaed for a closed-door deposition but insisted that any testimony he give before Congress be public in defiance of the lawmakers.

Hunter Biden said during a press conference on the Capitol grounds that he would testify publicly but did not want to do so behind closed doors out of concern that his words would be manipulated by Republicans. In response, Republicans said they would look into contempt proceedings.

Later that day, the House formally voted to authorize an impeachment inquiry into the president.

The party-line 221-212 vote saw all of the chamber's Republicans line up in support of the investigation, despite a lack of evidence that Biden has crossed a critical impeachment threshold, namely committing what the Constitution describes as "high crimes and misdemeanors" while in office. All Democrats were opposed.

But it is not at all clear into what matters the impeachment inquiry will delve. A roughly year-long investigation into the Biden family's business dealings has so far failed to produce solid evidence of wrongdoing.