File photo taken on Oct. 25, 2019 shows U.S. President Donald Trump speaking to reporters before leaving the White House in Washington D.C., the United States. (Photo by Ting Shen/Xinhua)

 
The US House of Representatives will vote this week on a resolution intended to affirm an impeachment inquiry against President Donald Trump and relevant procedures, Speaker Nancy Pelosi said on Monday, as a standoff with the administration was deepening.

"This week, we will bring a resolution to the Floor that affirms the ongoing, existing investigation that is currently being conducted by our committees as part of this impeachment inquiry, including all requests for documents, subpoenas for records and testimony, and any other investigative steps previously taken or to be taken as part of this investigation," Pelosi wrote in a letter to House Democrats.

The California Democrat said that they are "taking this step to eliminate any doubt as to whether the Trump Administration may withhold documents, prevent witness testimony, disregard duly authorized subpoenas, or continue obstructing the House of Representatives."

The resolution will establish "the procedure for hearings that are open to the American people, authorizes the disclosure of deposition transcripts, outlines procedures to transfer evidence to the Judiciary Committee as it considers potential articles of impeachment, and sets forth due process rights for the President and his Counsel," she added.

The text of the resolution has yet to be released but the resolution will reportedly hit the House floor on Thursday.

White House press secretary Stephanie Grisham said in a statement that they "won't be able to comment fully until we see the actual text" while accusing Democrats of "conducting an unauthorized impeachment proceeding, refusing to give the President due process."

"Their secret, shady, closed door depositions are completely and irreversibly illegitimate," she added.

The impeachment inquiry into Trump was initiated last month by Pelosi after an anonymous whistleblower had raised concern about the president's interactions with Ukraine.

Trump was alleged to have abused power by using a military aid that Congress approved to pressure Ukrainian President Volodymyr Zelensky into investigating former US Vice President Joe Biden, the leading 2020 Democratic presidential candidate, so as to help his re-election campaign.

The White House has said it will not provide documents or witnesses to House investigators because it considered the impeachment inquiry unfair and illegitimate.

In a tweet on Monday, House Minority Leader Kevin McCarthy called Pelosi's proposed resolution "an admission that this process has been botched from the start."

The California Republican also vowed not to legitimize the impeachment inquiry.

Democrats, who has a majority in the House, have argued that there is no need to hold a full House vote to authorize the inquiry, citing the nation's Constitution stating that the lower chamber "shall have the sole Power of Impeachment."

Trump has denied any wrongdoing and has urged more efforts from Republicans to defend him and challenge the impeachment inquiry, as depositions are turning to the White House and a series of witnesses have testified behind closed doors before House panels leading the investigation.

Before leaving for a visit to Chicago, Illinois on Monday morning, Trump defended his phone call with Zelensky while lashing out at Democrats over the impeachment inquiry, when speaking to reporters at Joint Base Andrews in Prince George's County, Maryland.

"We had a very good conversation with the Ukrainian president. The conversation was perfect," he said. "They tried to take that conversation and make it into a big scandal."

Pelosi's letter came hours after Charles Kupperman, a former White House national security aide, failed to show up for a scheduled deposition on Monday.

Kupperman, who had been subpoenaed to testify before House impeachment investigators, was expected to skip the deposition, as his attorney has asked a federal court for guidance on whether his appearance is legally required.

House Intelligence Committee Chairman Adam Schiff, who's leading the Trump impeachment inquiry, threatened charge Kupperman with contempt.

The chairman said that he believes Kupperman's testimony would corroborate allegations that other witnesses have made, while stressing that the impeachment inquiry will "move forward" even if witnesses don't appear.

Kupperman, deputy to former National Security Adviser John Bolton, was reportedly on a July phone call between Trump and Zelensky that is at the center of a whistleblower complaint that led to the impeachment inquiry.

Beloved to be a key witness in impeachment inquiry, Kupperman left his post several days after Bolton's abrupt departure from the White House last month.