WASHINGTON -- Matthew Whitaker's future at the helm of the Justice Department appeared uncertain at best Friday as President Donald Trump denied even knowing the man he had named acting attorney general just two days earlier. The Senate's top Republican predicted a permanent replacement could be named soon for Whitaker, who is now overseeing the Trump-Russia probe.

The comments from Trump and Senate Majority Leader Mitch McConnell came as Whitaker's past business ties and remarks on special counsel Robert Mueller's Russia investigation and other topics were drawing scrutiny from Democrats and ethics groups.

Speaking to reporters Friday, Trump said, "I don't know Matt Whitaker." That contradicted Trump's remarks on Fox News last month, when he called Whitaker "a great guy" and said, "I mean, I know Matt Whitaker."

McConnell, meanwhile, said, "I think this will be a very interim AG." Another Republican senator, Susan Collins of Maine, said she was concerned by some of Whitaker's past comments and called for legislation that would place limits on his ability to fire special counsel Mueller. That would include specifying that only a Senate-confirmed Justice Department official -- which Whitaker is not -- could dismiss Mueller.

Whitaker, a Republican Party loyalist and chief of staff to just-ousted Attorney General Jeff Sessions, was elevated Wednesday after his boss was forced from his job by Trump. The new position handed him oversight of Mueller's investigation into possible ties between Russia and Trump's 2016 presidential campaign.

Since Wednesday, Whitaker has faced pressure from Democrats to recuse himself from overseeing Mueller based on critical comments he made about the investigation before joining the Justice Department last year.

Those included an op-ed article in which he said Mueller would be straying outside his mandate if he investigated Trump family finances and a radio interview in which he maintained there was no evidence of collusion between the Kremlin and the Trump campaign. He also tweeted an ex-prosecutor's opinion piece that described a "Mueller lynch mob," which he said was "worth a read."

There have also been reports about Whitaker's past comments questioning the power and reach of the federal judiciary, and about his ties to an invention-promotion company that was accused of misleading investors. The Wall Street Journal on Friday published an email revealing an FBI investigation into the company, World Patent Marketing Inc. The July 10, 2017, email was from an FBI victims' specialist to someone who the newspaper said was an alleged victim of the company. A Justice Department spokeswoman told the Journal that Whitaker was "not aware of any fraudulent activity."

Whitaker himself stayed out of the public debate Friday. He sent a department-wide note after his appointment in which he said, "As we move forward, I am committed to leading a fair Department with the highest ethical standards, that upholds the rule of law, and seeks justice for all Americans."

Legal scholars are debating the constitutionality of his appointment, with some lawyers saying it is illegal because he has not been confirmed by the Senate.

Despite Trump's current distancing himself from Whitaker, two Republicans close to the president said he had enjoyed Whitaker's TV appearances and the two had struck a bond. Those TV appearances included one on CNN in which Whitaker suggested that the Mueller probe could be starved of resources.

Trump told associates that he felt Whitaker would be "loyal" and would not have recused himself from the Russia probe as Sessions had done, according to the Republicans, who were not authorized to speak publicly about private conversations and commented only on condition of anonymity.

On Friday, Trump said he had not spoken with Whitaker about Mueller's investigation, which until now has been overseen by Deputy Attorney General Rod Rosenstein.

Rosenstein told reporters Friday that based on his experiences with Whitaker, "I think he's a superb choice for attorney general."

Of the scrutiny Whitaker is facing, Trump said, "It's a shame that no matter who I put in they go after."

"He was very, very highly thought of, and still is highly thought of, but this only comes up because anybody that works for me, they do a number on them," Trump said.

In Kentucky, meanwhile, McConnell said he expects Trump to nominate a new permanent attorney general "pretty quickly." McConnell said he expects Whitaker to be "a very interim" appointee.

"The president has said repeatedly he's not going to dismiss the Mueller investigation," McConnell told reporters at Kentucky's Capitol. "He's said repeatedly it's going to be allowed to finish. That also happens to be my view."

Trump has not said whom he will nominate to permanently replace Sessions.

Former New Jersey Gov. Chris Christie is said to be a candidate, along with Labor Secretary Alex Acosta and Health and Human Services Secretary Alex Azar, among others.

Trump told reporters he has not discussed the post with Christie, who he said was "a friend of mine" and "a good man."

Associated Press writer Bruce Schreiner contributed to this report from Frankfort, Kentucky.