Serial liars, yes, ok - point taken.
I was looking at it more in terms of "degree and duration of criminality", on which you really can't compare Nixon with Madoff?!
You might include Clinton, too, and perhaps even a fortiori, if "serial liars" is your perspective?
(I hate to say it, but I probably even agree with your equivocation about Berlesconi, on that front.)
Of course, Clinton lied when he said I did not have sex with that woman. In the end it was lying about personal matters under oath that got him impeached. But the public said, wait a g.d. minute here, those are questions you shouldn't have been asking in the first place! It is none of your g.d. business.
Nixon's lies were about crimes of the most serious sort imaginable: He campaigned on a promise of peace with honor. American voters believed that meant peace. Instead it meant an escalation of the Vietnam war, and stepped up involvement in the civil wars in Laos and Cambodia, much of which was at least initially hidden from the American public. We bombed both Laos and Cambodia. Later we sent troops, then admitted it when it could no longer be hidden. In Laos, we bombed one of the most etherably beautiful places on Earth, the plain of Jars. From 1964 to 1973, US forces flew 580,944 missions over Laos. We dropped the equivalent of a B52-load of bombs every eight minutes for nine years, much of it on the plain of Jars. Long after it was clear the war in Vietnam could not be won Nixon callously caused thousands more lives to be lost unnecessarily, including thousands of American lives and hundreds of thousands of Vietnamese lives.
Truman, Eisenhower, Kennedy and Johnson all made mistakes with regard to U.S. Indochina policy. Both Johnson and General Westmorland fed lies to the American Press regarding the prospects for an outcome favorable to U.S. interests in Vietnam. Johnson at least had the sense to ultimately realize the war could not be won, and it was becoming hugely unpopular among the American public. Recognition of certain failure contributed to Johnson's decision not to seek re-election. Nixon disregarded all that had been learned from 24 years of failed Indochina policy, and accelerated the offensive in Vietnam in a losing effort..
After the break-in at the Watergate, Nixon was directly involved in raising bag money to buy silence from witnesses, in an attempt to Bribe the Judge sitting in the Daniel Ellsberg trial, and he was complicit in the break-in into Ellsberg's psychiatrist's office. Nixon told his White House confidants that "When the President does it it is not illegal. What arrogance! Nixon knew nothing of the Watergate break-in before hand and could have taken the high road and just fired everyone involved, instead he personally led the cover-up effort.
In my post above I said Johnson thought the war could be won and Nixon realized it was lost. Here in this post I say the opposite. This has to do with timing. The record indicates that initially Johnson did believed the war could be won but only came to the realization that it could not be late in his Presidency. Nixon had the arrogance to believe that he could prevail where others had failed and that by stepping up the bombing he could force the Vietnamese to accept his terms. After it became clear to everyone that there was no possibility of bombing the Vietnamese into accepting U.S. Terms, Nixon stubbornly persisted in a vain attempt to save face, even after it was clear he could not force the North Vietnamese to agree to his conditions . He continued to lie to the American public long after he realized that he was not going to achieve his version of peace with honor.