President Trump told reporters Wednesday he did not "specifically" authorize the mission in Niger that left four soldiers dead, as he gave a wide-ranging impromptu press conference outside the White House with reporters before departing for Dallas.

The Niger mission has come under increasing scrutiny, as questions linger about how four U.S. soldiers died in the ambush. Asked if he authorized that mission that has drawn an intense level, Mr. Trump said, "No I didn't. Not specifically. But I have generals that are great generals, great fighters, these are warriors." This week, Mr. Trump has continued to grapple with the fallout from his call to the widow of Sgt. La David Johnson, one of the four soldiers who died.

"I was extremely nice to her, I was extremely courteous, as I was to everyone else," Mr. Trump said.

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Mr. Trump was also asked for his reaction to a Tuesday evening Washington Post report that the Clinton campaign and the Democratic National Committee funded research that led to the now-infamous Trump dossier. Mr. Trump called the dossier report a "disgrace."

"I think it's very sad what they've done with this fake dossier," Mr. Trump said. "It was made up and i understand they made a tremendous amount of money, Hillary Clinton always denied it, Democrats always denied it. And now only because it's going to come out in a court case case they said, yes, they did it. They admitted it and they are embarrassed by it. I think it's a disgrace, it's just really a very sad commentary on politics in this country."

The president also reacted to Sen. Jeff Flake's Tuesday announcement that he will not run for re-election, as the Arizona Republican made a number of searing critiques aimed at the president and at other Republicans who refuse to challenge his behavior. Mr. Trump said the Republican Party has "great unity," but didn't miss an opportunity to criticize Flake.

"He was up against me before he ever knew me," Mr. Trump said. "He wrote a book about me before I ever met him, before I ever heard his name. His poll numbers in Arizona are so low that he couldn't win and I don't blame him for leaving. I think he did the right thing for himself. But if you know, long before he ever knew me, during the campaign, even before the campaign, he came out with this horrible book, and I said, 'Who is this guy?' In fact, I remembered, the first time I saw him on television I had not -- nobody knew me in terms of politics."

The president is also facing a less-than-smooth legislative battle on tax reform, as his party disagrees over the details of the bill the White House insists will be on the president's desk by the end of the year. Mr. Trump did not take the possibility of 401(k)-related changes off the table, amid reports that Republicans are considering changes to tax deductions for retirement savings. The president said 401(k) plans are "very important to me," but also said the could be used in the negotiation process.

Asked if he should be more civil, the president slapped at the press and touted his own intelligence.

"Well, I think the press makes me more uncivil than I am," Mr. Trump said. "You know people don't understand. I went to an Ivy League college. I was a nice student. I did very well. I'm a very intelligent person. The fact is, I think, I really believe -- I think the press creates a different image of Donald Trump than the real person."

In Dallas, Mr. Trump will attend a Republican fundraiser billed as "An Evening with Donald Trump," with tickets costing between $2,700 and $100,000 per person.

CBS News' Jacqueline Alemany contributed to this report.