Rep. Elijah Cummings threatened Tuesday to hold former White House adviser Carl Kline in contempt of Congress for defying a subpoena ordering him to testify about his role allegedly covering up wrongdoing in the Trump administration’s White House security clearance process.

President Donald Trump’s White House counsel directed Kline in a letter earlier this week not to comply with the subpoena. Kline did not appear for his scheduled deposition.

“It appears that the President believes that the Constitution does not apply to his White House, that he may order officials at will to violate their legal obligations, and that he may obstruct attempts by Congress to conduct oversight,” Cummings, who chairs the House Committee on Oversight and Reform, said in a statement Tuesday.

The Maryland Democrat, whose committee is investigating allegations of impropriety and nepotism in the White House’s security clearance process, said he will consult with House counsel and other members on his panel about scheduling a vote on contempt.

“I hope that Mr. Kline, in close consultation with his personal attorney, will carefully review his legal obligations, reconsider his refusal to appear, and begin cooperating with the Committee’s investigation,” Cummings said.

If Kline and the administration challenge an eventual contempt of Congress suit, that could set up a momentous legal battle between the legislative and executive branches.

Earlier this year, an 18-year employee for the Executive Office of the President who managed security clearance adjudications under Kline, told the committee that clearance decisions “were not always adjudicated in the best interest of national security.” The administration overturned more than two dozen adjudications made by career security officials, the whistleblower, Tricia Newbold, told the Oversight panel.

Newbold has accused Kline of retaliating against her for blowing the whistle on possible abuse of the White House security clearance policy.

“As the Committee with primary jurisdiction over the Whistleblower Protection Act, we take extremely seriously our responsibility to investigate these allegations and to protect the rights of all whistleblowers who come before Congress,” Cummings said Tuesday.

Republicans have argued that Trump is well within his rights as president to issue security clearances to anyone he pleases, regardless of career intelligence officials’ advice.

They balked at Cummings’ threat Tuesday to hold Kline in contempt.

“When faced with choice of cooperation or confrontation, Chairman Cummings picked confrontation,” a spokesman for Ohio Rep. Jim Jordan, the top Republican on the Oversight panel, said in a statement Tuesday.

Cummings “rushed to a subpoena in his insatiable quest to sully the White House. In doing so, he trampled over the normally deliberate and reasonable processes by which the Committee operates. This is a shame,” Jordan’s spokesman said.

The White House has stonewalled Democrats’ probe into those allegations, Cummings has said, failing to provide “a single piece of paper” to the committee.