Claims that Donald Trump shared official secrets with Russia are the most serious ever levelled against a sitting president, a Harvard law professor says.
"It’s not illegal, it’s not impeachable, but it’s totally and completely wrong," Alan Dershowitz told Nine to Noon.
US media outlets are reporting that the information Mr Trump passed on to the Russians originally came from Israeli intelligence - that ISIS was developing a way to get bombs on planes using laptops.
Analysts say that if the claims are true, Israel would be worried given Russia could make the information available to its ally, Iran - Israel's main threat in the Middle East.
The development comes just days before Mr Trump is due to visit Israel.
Prof Dershowitz said the president’s actions and the subsequent leak to the Washington Post have jeopardised high-level intelligence.
"What he did was completely legal, just as it would be legal for him to tweet the nuclear codes to anyone in the world who wanted them."
He said Israel had a long history of getting agents into high-level positions.
"At great risk, Israel has managed to get into ISIS and in one fell swoop the president tells Russia the source of the information was Israel and the city in which the information was gathered ... we know the president provided the name of the city."
He said the subsequent leak to the Washington Post meant ISIS now knows what Russia knows.
"If there is this person [embedded in ISIS] he's probably dead by now, if not he has tried to escape and no longer can provide secrets that can help the world."
Prof Dershowitz said it was possible Mr Trump did not even know the source of the information was from an ally.
"This president doesn't get briefed every day. He thinks he knows more than the intelligence agencies do when he went and revealed this information to the Russians.
"He said the president had poor "impulse control" and would not have been able to resist telling the Russians what he knew.
Now however, Mr Trump's own security people and foreign allies will be worried about how much to tell the president and his ability to keep tight-lipped. They may choose to withhold information from the President of the United States.
"To cut off those kinds of sources is to cut off important information that can save an enormous number of innocent lives," Prof Dershowitz said