"Orders must have come from the top. The U.S. must not be complicit in an effort to cover-up this heinous crime," he said.

And Sen.(D-Md.), the chairman of the Senate Democrats' campaign arm, said that Trump's suggestion "defied reality."

"President Trump’s response to Jamal Khashoggi’s disappearance reveals a man more willing to trust authoritarian leaders than reliable intelligence," Kaine said

Sen.(D-Va.), another member of the panel, added that Trump's rhetoric was "insulting."

"Been hearing the ridiculous 'rogue killers' theory was where the Saudis would go with this. Absolutely extaordinary they were able to enlist the President of the United States as their PR agent to float it," Murphy said in a tweet

Sen.(D-Conn.), a member of the Foreign Relations Committee, said that by floating the idea that "rogue killers" were to blame, Trump had been enlisted as a "PR agent" for Saudi Arabia.

Senate Democrats quickly hit back Monday at's suggestion that "rogue killers" could be behind the disappearance of a U.S.-based journalist, calling his remarks "insulting" and comparing him to a "PR agent" for Saudi Arabia.Trump told reporters at the White House that "rogue killers," and not Saudi officials, could be responsible for Washington Post contributor Jamal Khashoggi's disappearance, noting that he had just spoken with Saudi King Salman, who denied Riyadh's involvement.

President Trump’s suggestion that Khashoggi’s elaborately planned murder in the Saudi’s own consulate was orchestrated by “rogue killers” defies reality. Orders must have come from the top. The U.S. must not be complicit in an effort to cover-up this heinous crime. https://t.co/qJkBZ1sPG8

Khashoggi has been missing since Oct. 2, when he entered the Saudi consulate in Istanbul to get paperwork needed for his marriage. Turkish officials have said they believe Khashoggi was killed and dismembered inside the consulate on orders of the government in Riyadh.

Saudi Arabia has denied wrongdoing and said Khashoggi left the consulate shortly after he arrived, but hasn't provided any evidence to support that claim.

Trump on Monday said King Salman's denial "was very, very strong" and it did not seem as if "there was a question" in the king's mind about his claim Saudi Arabia was not involved.

But Khashoggi's disappearance has put a new strain on the U.S.-Saudi relationship, with Trump facing bipartisan pressure from Congress to enact swift punishment on Riyadh if officials there can't provide evidence that Khashoggi is still alive.