President Trump has officially embraced Richard Nixon's infamous view of presidential authority: "When the president does it, that means that it is not illegal." That is the clear implication of a letter Trump's lawyers sent to Special Counsel Robert Mueller, which made sweeping claims about the president's legal immunity from prosecution.

Very disturbing indeed — but it is a reflection of the basic failure of the American constitutional structure to perform as advertised. Instead of restricting the growth of tyranny, the Constitution's separation of powers is enabling the coronation of our own mad king.

So what's in Trump's letter? The document contains many sweeping legal claims, but probably the boldest is that even if Trump ordered the termination of the Mueller investigation into himself and his associates, it would be fine: "[E]ven assuming, arguendo, that the president did order the termination of an investigation … this could not constitute obstruction of justice." That fits with an earlier argument in the letter, which asserts that Trump's actions, "by virtue of his position as the chief law enforcement officer, could neither constitutionally nor legally constitute obstruction because that would amount to him obstructing himself" (l'etat, c'est moi, as the man said).

Rudy Giuliani, now one of Trump's lawyers, gave concrete form to that theory, asserting to HuffPost on Sunday that "in no case can [Trump] be subpoenaed or indicted" — not even if he straight-up murdered former FBI Director James Comey. The only restraint on Trump's behavior, Giuliani said, was impeachment. Trump himself apparently agrees, tweeting that he has the "absolute right to PARDON myself," but would not do so (at least for the moment).

The implications are potentially sweeping. If Trump can pardon anyone, including himself, and shut down any investigation, then he has a free pass to break any federal law. He could take bribes, dole out appointments to his friends, or otherwise abuse his powers of office, and then simply dissolve any investigations and pardon anyone who gets caught. And since D.C. laws are federal laws, if Congress convenes an impeachment hearing, then by this logic there is nothing stopping Trump from ordering the murder of the committee members, and then pardoning the assassins.

All this would no doubt have horrified the drafters of the Constitution. Even Alexander Hamilton, who had strong authoritarian tendencies — he admired the British monarchy, and tried to replicate what he saw as its better parts in the U.S. — made greater accountability one of his primary arguments for a strong executive. In Federalist 70, he argues against an executive council in part because it tends to obscure responsibility: "[T]he plurality of the Executive tends to deprive the people of … the opportunity of discovering with facility and clearness the misconduct of the persons they trust, in order either to their removal from office or to their actual punishment in cases which admit of it."

Obviously, if the president can simply prevent all investigation or punishment into his own crimes or those of his family and associates, the people will have no such opportunity.

The way the Constitution is supposed to work, of course, is that if the president behaves corruptly, then Congress will remove him from office. That is supposedly the whole point of dividing powers between the executive and the legislative, and there between the House and the Senate: "Ambition must be made to counteract ambition," as James Madison wrote in Federalist 51. And indeed, that was kinda-sorta how things worked for most of American history — Nixon resigned before being removed, and previous presidents at least kept their corruption within certain boundaries. But at the same time, all that separation of powers meant American government was often divided between parties and barely able to deal with severe problems. Executive power flowed into the gap left by congressional inaction.

In addition, the system was also helped by the partial multi-party tendency that prevailed from the end of the Civil War until about the 1990s, where each party had a left and right wing, thus making legislative dealmaking, and a self-identity of Congress that was independent from the president, easier.

But as American political parties became more like European ones, with strong ideological identities and rigorous partisan discipline, legislative deadlock skyrocketed, and the independent identity of Congress eroded. And probably most importantly, one of two parties has been recently dominated by an extremist revanchist movement.

As a result, the whole complicated American constitutional edifice designed to prevent tyranny and corruption is melting to nothing before the Trump crisis. His personal corruption alone should have removed him from office when he refused to divest himself of his businesses, or at least when he started blatantly enriching himself through the presidency. But nothing is happening, and there is absolutely no sign that Congress is going to start fulfilling its constitutional obligations absent huge changes in the 2018 midterms.

South Korea recently went through a corruption crisis maybe about half as bad as the one currently suffusing the American executive branch. The corrupt president, Park Geun-hye, was removed from office, and she and several top aides and allies were convicted and punished. To be fair, morality and healthy political parties were part of the reason why — the country also has a presidential system; Park lost power when her approval rating fell to single digits, and her own party turned on her. However, another factor was that South Korea has only one house in the legislature, and a handy mechanism to restore democratic legitimacy in case of a bad president — namely, snap elections.

That's what honest democratic countries do when their president is a crook. I increasingly suspect that without some serious changes to the Constitution, America will never again qualify.