Sen. Mitt Romney (R-Utah) told NBC News' Geoff Bennett on Monday that the Trump administration should make the whistleblower complaint that reportedly involves the president and Ukraine available to Congress, adding that it would be "very helpful to get [to] the bottom of the facts."

The big picture: Romney continues to be the only Republican senator to condemn allegations that Trump pressured Ukraine's president to investigate Joe Biden, tweeting on Sunday that the reports are "troubling in the extreme." Romney told NBC that it would be "up to the House to decide how to proceed" if the administration fails to release the whistleblower complaint.

On Monday, the Democratic chairs of the House Intelligence, Oversight and Foreign Affairs committees demanded that the State Department produce documents related to the Trump-Ukraine allegations, threatening a subpoena if the agency fails to comply.

Go deeper: Trump doubles down on defense of Ukraine conversation about Biden