The chairman of the US Senate Judiciary Committee has vowed to get to the bottom of allegations that discussions were held in 2017 on removing President Donald Trump from office.
Senator Lindsey Graham pledged to issue subpoenas "if that's what it takes".
Ex-acting FBI chief Andrew McCabe has said deputy US attorney general Rod Rosenstein discussed the numbers needed to invoke the 25th Amendment.
Mr Rosenstein has in the past denied discussing invoking the clause. The amendment provides for the removal of a president if deemed unfit.