I’d say the worst president was Lincoln. It was under him that the Fed Gov went from being merely an “umbrella” government with certain delegated powers, responsible to its creator, the States, to seizing more power than had been delegated to it, and actually dictating to its creator, the States. In other words, Lincoln turned the Constitution upside down. Instead of the Fed Gov being subservient to its creator, the States, after Lincoln, the States were subservient to the Fed Gov, at least practically. but not Constitutionally.
In second place would have to be FDR. He’s the guy that started a lot of this Federal welfare bullshit, such as Social Security. And he threatened the Supreme Court in order to pass many of his heretofore illegal schemes. And he also gave away half of Europe to Stalin at the Yalta conference.
My third place worse Pres would have to be Johnson. He greatly expanded Federal welfare with his “Great Society” programs. He’s also the guy who signed Kennedy’s 1965 Immigration law which has had the affect of allowing tens of millions of third world people to immigrate into the US.
Nixon? There’s no evidence that he even knew about the Watergate break-in. His great sin was covering it up. While he certainly was paranoid, at least he was competent on the job. My only gripe about Nixon was that he was such a liberal on domestic policy.