not quite 4 - Robert E. Lee

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There is a quote attributed to Robert E. Lee who fought for the U S in the Mexican War of 1845 and the Confederacy in the Civil War 1861-65. He was a highly respected General who won (among many others) the the Battle of Fredericksburg (13th December 1862) by placing his men in fortified positions and slaughtering the Yankee troops that Union General Burnside sent across an open field.
Afterwards he said: "It is well that war is so terrible - otherwise we would grow too fond of it."

Seems to me that this is one of those quotes that doesn't quite work because if it wasn't "so terrible", then there wouldn't be any problem with "growing too fond of it."

PS Eight months later on the 3rd day at Gettysberg Lee repeated Burnside's mistake and had Gen George Pickett launch thousands of Rebels across an open field against a greater number of men behind a stone wall. When the Yankees drove the surviving Rebels back across the field they banged on the wall and chanted: "Fredricksburg! Fredricksburg! Fredricksburg!"

PPS I suppose that you would have to say that Lee's decision was worse than Burnside's since it came later. But surely the worst would be those WWI generals who had fifty years to study that war and even greater firepower and still they issued those orders to go "over the top" and across those open fields. Apparently, they had never taken notice of what had happened in "the colonies".
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not quite 3 bad predictions

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LeRoy Pope Walker, from Alabama, was the first Secretary of War of the Confederate States of America. After the initial secession of seven states, he was a commissioner to Tennessee to urge them to withdraw as well. In denigrating the possibility that the Union would attempt to coerce the South as a result of secession he stated that,

“All of the blood shed in the (threatened) Civil War could be wiped up with a pocket handkerchief.”

The death toll was over 600,000 from a country of about 30 million.
A comparable death toll in the country today would be 6,000,000.
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Not quite 2 John Kennedy

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I don’t know if he was the originator of it but John F Kennedy said to a distinguished group at the White House one day.
"I think this is the most extraordinary collection of talent, of human knowledge, that has ever been gathered at the White House - with the possible exception of when Thomas Jefferson dined alone."
It is a cute idea but as a saying it doesn’t really work. Obviously you would have a greater collection whenever TJ had Secretary Madison and the rest in for a cabinet meeting.

not quite 1 - Able was I ere I saw Elba

The title is perhaps the most famous English palindrome ( = an expression that reads the same forward and backward). Supposedly it was by Napoleon about his first exile. But Napoleon’s native languages were Italian and French and though he learned a little English the English people were his lifelong enemies? Is there any evidence that Napoleon actually composed it, uttered it or ever even heard it?