Warren Harding - Connolly wrote, "Warren G. Harding is generally regarded as the worst president ever. He was disappointing from the get-go, as the very basis of his campaign was boring. Harding ran on the promise of a 'return to normalcy,' which he (somehow) felt people craved following Woodrow Wilson's bold and visionary term."
The fact that just about everyone except political detractors of the current President Bush consider Harding the worst president ever keeps him off the forgotten list. The worst will always be remembered. (Although James Buchanan is often ranked as worse than Harding should not be forgotten either.)
Chester Arthur - Connolly wrote, "Most people don't know ol' Chesty for anything other than his mammoth moustache. But he should be remembered as a guy who rose to the occasion."
And the occasion he arose to was a massive reform of the civil service system which greatly helped some of the presidents who followed Arthur in office. Presidential historians often reference him and he is actually ranked higher on the list of presidents by historians than the "forgotten" tag would indicate.
John Tyler - Connolly wrote, "John Tyler was up against it from the start. For one thing, he only got to be president because he was the VP under William Henry Harrison, who died of pneumonia following his inauguration speech. Let's put it this way: When your nicknames include 'His Accidency,' you're not destined to make a splash."
As Tyler clearly established that a vice-president assuming a vacant presidential post was actually the president, his actions were huge. The "his accidency" reference comes from those who believed that a vice-president in this situation was actually an "acting" president. Presidents such as Truman and Ford have much to thank Tyler for. Further, Tyler is the only American President to have actually openly committed an act of treason against the USA when he served in the Confederate rebel government. Forgotten? Hardly.
I can not disagree with Connoly putting Fillmore, Hayes, or Van Buren on the list. Hoover is debatable. Why did he not include Franklin Pierce, William Henry Harrison, or James Garfield on the list though? These men are much more forgotten by historians as presidents.