Donald Trump pleaded ignorance on Friday about a senior GOP senator dumping hotel stocks that since have lost value due to the coronavirus outbreak, but then immediately admitted to knowing a Democratic lawmaker also sold stocks before the virus hit US soil.

"I'm not aware of it," the Republican president said when asked about Senate Intelligence Committee Chairman Richard Burr selling hotel stocks around the time lawmakers began getting classified briefings about the virus and its potential damaging blow to the US economy.

Mr Burr on Friday tried to explain away his move by saying he got the idea by watching CNBC, adding he has referred the matter to the Senate Ethics Committee for a full review. Because that process likely will take months, Mr Burr's first major political scandal could simply be lost to the daily deluge of COVID-19 developments.

But almost as soon as the president claimed to not know anything about Mr Burr's plight, he asked a reporter why she wasn't mentioned in her question that a Democratic senator also dumped stocks before the virus outbreak.

He was referring to Sen. Dianne Feinstein, a senior California Democrat, who has said the stock portfolio owned be she and her husband is managed by a blind trust.

"I saw some names. I know all of them," Trump said after first claiming no knowledge of the situation, first reported by ProPublica and others.

Even before the Ethics Committee started its investigation, the president again got in front of typical Washington processes for finding the truth, appearing eager to defend Mr Burr, who has become a close ally, he said this: "they certainly did nothing wrong."

And, as always, Mr Trump went on the attack, trying to paint the reporter as biased against all Republicans.

"It's interesting that you mention two people, but you don't mention one that happens to be a Democrat," he said.

The reporter then clarified her question to focus on whether "any senator" should be investigated if they sold stocks while possessing knowledge about a coming likely crisis while not warning their constituents of the financial danger.