Washington (CNN) President Donald Trump's use of executive privilege to block former White House counsel Don McGahn from complying with a congressional subpoena "is always an option," White House counselor Kellyanne Conway said Sunday.

"Executive privilege is always an option, it's always on the table. But Don McGahn has already talked under oath for 30 hours. And this is just presidential harassment," Conway told CNN's Jake Tapper on "State of the Union," adding that it's Trump's "right" to use the power.

Conway's comments come nearly a week after the House Judiciary Committee served McGahn with a subpoena as part of its investigation into obstruction of justice, a move to bring in a key player with direct knowledge about Trump's efforts to undermine the Russia probe, which were outlined in special counsel Robert Mueller's report on Russian interference in the 2016 election.

Shortly after the subpoena was issued, CNN learned that the White House may seek to prevent McGahn from complying with it. A source familiar with the idea said the President could assert executive privilege over specific aspects if McGahn testifies, but noted that discussions are not that far along yet and added that other measures are still being considered.

McGahn's testimony is still being negotiated with the committee, and he could be a key test case for the committee's broader investigation into possible corruption, abuse of power and obstruction of justice, in which the panel is likely to seek interviews with numerous White House officials.

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