The infamous Watergate scandal "pales" in comparison to the allegations about the Trump administration's links to Russia, former United States intelligence chief James Clapper has said in an explosive set of remarks in Canberra.

Mr Clapper, who served as Director of National Intelligence under Barack Obama and in senior roles with Republican leaders as well, also said he would "understand" if US allies such as Australia withheld intelligence from American counterparts because of Mr Trump's demonstrated lack of discretion with such sensitive secrets.

The 50-year veteran of the military and the intelligence community painted a picture of disconcerting dysfunction in Washington with "assaults on American institutions coming from both external and internal sources" and most strikingly said the Trump-Russia links were much worse than the notorious scandal that toppled former US president Richard Nixon in the 1970s.

"I lived through Watergate. I was on active duty then in the Air Force as a young officer," Mr Clapper said following a speech to the National Press Club in Canberra. "It was a scary time . . . I have to say, though, that I think you compare the two that Watergate pales really in my view compared to what we're confronting now."