WASHINGTON — House Democrats say the White House's decision to withhold information from a key committee is impeding their investigation into the issuance of security clearances for White House officials and are considering a subpoena for the documents and, potentially, more witnesses.

Democrats' reactions came after a day of questioning behind closed-doors of Carl Kline, the former White House official in charge of issuing security clearances, and after the Trump administration refused to provide the committee with documents they requested about the process.

"We are at a point right now where we are at a critical time in our country's history because we have a president who is acting like a king and who has instructed his folks not to give us one document and not allow us to have witnesses," House Oversight and Reform Committee Chairman Elijah Cummings said.

The committee is investigating the approval of security clearances for at least 25 administration officials despite recommendations not to as well alleged retaliation against staffers who raised objections, according to whistleblower Tricia Newbold, a security specialist in the White House.

Democrats said Kline did not provide specific details to their questions.

“I think that the White House (is) basically instructing the witness not to answer questions that are very pertinent to our inquiries, our legitimate inquiries, our legitimate and valid legislative purposes,” Rep. Raja Krisnamoorthi, D-Ill., said.

Democrats’ frustration has risen as the president and his administration have vowed to stonewall congressional requests for documents and testimony on a variety of issues, including into President Trump’s finances, taxes and how security clearances were approved. They are threatening to hold White House officials in contempt and to take action if Congress continues to be ignored.

Republicans disputed Democrats' assessment, saying that Kline was forthcoming and that Kline said that the president did not direct him to give security clearances.

“A lot of the previously published reports of what happened was certainly not authenticated by the testimony I heard today,” Rep. Mark Meadows, R-N.C., said. “I think once the transcript is released you'll get to see very different side of what actually transpired.”

But Democrats say that Kline refused to answer questions about individual security clearances, including to Trump's son-in-law and adviser Jared Kushner, who was given a security clearance despite alleged recommendations against it.

Just hours before Kline was scheduled to appear before the committee, White House lawyer Pat Cipollone sent a nine-page letter to Committee Chairman Elijah Cummings, D-Md., outlining reasons the White House will not hand over documents pertaining to security clearances. The documents are outside of their legislative prerogative and the request interferes with the president’s authority to make decisions as commander-in-chief, Cippollone argued in the letter obtained by NBC News.

“Obviously, the committee's demands fall well outside the realm of legitimate congressional information requests,” Cipollone writes in the letter. “Congress does not have the power to target individuals for the sake of ‘exposing’ alleged derogatory information to the public.”

“The Committee is also attempting to obtain confidential information relating to the President's exercise of his authority as Commander-in-Chief to grant or deny security clearances and to choose his advisors,” Cipollone adds. “Indeed, it is difficult to fathom a situation in which the President is entitled to greater constitutional protection from congressional intrusion.”

Chairman Cummings said that the White House is simply stonewalling the investigation.

“The White House Counsel and the president have made a decision, they don't really want us to interview anybody out of the White House and they made it clear through their actions this morning that although we need documents and we have requested them in a proper way that they are blocking the information and people,” Cummings said.

Kline’s closed-door testimony comes after the White House and the administration settled a dispute that previously delayed his appearance.

This is not the first showdown between the president and the committee. The president is suing accounting firm Mazars to prevent them from handing over Trump’s financial documents. And the Justice Department is preventing Deputy assistant secretary John Gore from testifying on adding a citizenship question to the census.

House Democrats on the Judiciary Committee are at loggerheads with Attorney General Bill Barr over scheduled testimony Thursday. The Department of Justice is resisting new committee requirements that Barr be asked questions by committee lawyers after the lawmakers ask their questions.