Mr. Trump promised unspecified punishment if Saudi Arabia is implicated in killing the journalist. "We just went through that with Justice Kavanaugh and he was innocent all the way as far as I'm concerned", he told Associated Press.
He told the AP news agency that Riyadh was being treated as "guilty until proven innocent". I don't like that.
Many members of the US Congress, which has long had a testy relationship with Saudi Arabia, have issued strong criticism of the kingdom over the case.
As Florida Sen. Marco Rubio said Tuesday: "There isn't enough money in the world to purchase back our credibility on human rights and the way nations should conduct themselves".
While Trump and the Saudis appear on the same page about "rogue killers", Erdogan reminded observers on Tuesday that Turkey remained in control of the facts of the case as its investigators continued to uncover potentially damning information.
"The king firmly denied any knowledge of it", Trump told reporters after speaking with King Salman.
Trump said he didn't "want to get into (Salman's) mind", but he added, "it sounded to me like maybe these could have been rogue killers".
Pompeo was dispatched by Trump to Riyadh and Turkey over the Khashoggi case.
The crown prince said in an interview with Bloomberg News a day after Khashoggi's disappearance that he believed the journalist had left Saudi Arabia's consulate in Istanbul alive after entering on October 2.
Secretary of State Mike Pompeo met with King Salman on Tuesday morning, before meeting with the Crown Prince.
A Turkish forensic stands next to the Saudi flag, on the roof of the Saudi Arabia's consulate in Istanbul.
Trump Speaks to Saudi King, Sends Pompeo for Follow-Up
The exchange dropped by over 500 points, then clawed back some of the losses, ending the day down more than 4 per cent. The broadcaster said it wasn't immediately clear if those who arrived were Turkish or Saudi representatives.
But that has now been delayed because no Saudi official can be present for what has been billed as a joint investigation, Turkish officials say.
"The consul's behavior and approach drew reaction after Khashoggi disappeared", Cavusoglu said - criticizing the way the consul behaved in a Reuters tour of the consulate - "especially how he opened the cabinets saying "look he is not here" as if mocking people, behaving disrespectfully".
In the meantime, there were signs at home that Mr. Trump's party was growing uncomfortable with his willingness to defend the Saudis.
US President Donald Trump said Tuesday he had spoken with Saudi Crown Prince Mohammed bin Salman and been assured that a "full" probe into the disappearance of a critical journalist was underway.
Senator Lindsey Graham, a Republican close to Trump, has called Prince Mohammed "a wrecking ball" and accused him of ordering Khashoggi's murder.
How the crown prince, often referred to as MBS, emerges when the dust settles over Khashoggi's disappearance is a test of how the West will deal with Saudi Arabia in the future. Late in the day, there were published reports that the Saudis were preparing to concede that Khashoggi, a US -based Saudi contributor to The Washington Post, had been killed in an interrogation gone wrong.
Concern over Khashoggi's disappearance has seen media organizations and a growing number of guests pull out of a "Davos in the Desert" investment conference set for October 23-25, which has become the biggest show for investors to promote Prince Mohammed's reform vision.
Gardiner said, "The United States is supporting Saudi Arabia in its military efforts against Iranian backed Houthi rebels inside Yemen, so it's a very complex picture".
He said it was too early to say whether he endorsed other countries' actions.
Mr Khashoggi, a U.S. resident and critic of the Saudi regime, has been missing since 2 October when he visited the Saudi embassy in Istanbul to obtain documents.