I have said many things in my life that I regretted. Never, though, did I make these statements in a speech. A prepared remark holds more weight than spontaneous speech.
The people quoted below knew they would be quoted. Their words expressed their intent, at least when they spoke them (or wrote them). In some cases, a figure may have captured sentiments at a moment in time and then have had a change of heart, years later.
Albert Einstein, for example, urged President Franklin Roosevelt to develop a fission-based bomb, an atomic bomb. In 1939 he
wrote, persuasively,
In view of this situation you may think it desirable to have some permanent contact maintained between the Administration and the group of physicists working on chain reactions in America.
In 1954 he changed his mind. He
said to a friend that urging Roosevelt to develop the bomb was the "one great mistake of his life".
This famous scientist's about turn is one of the most somber in history.
Einstein, by Doris Ullman. 1934. 
Another, perhaps more consequential about face may be found in the words of Neville Chamberlain, Prime Minister of the United Kingdom in the years leading up to WW II. In 1938 he gave a speech to his nation in which he
expressed confidence in Hitler's promise to stop military aggression. Chamberlain announced:
This is the second time in our history that there has come back from Germany to Downing Street peace with honor. I believe it is peace for our time.
Chamberlain announcing peace agreement with Hitler. National Digital Archives Wydawnictwo Prasowe Kraków-Warszawa used under _1938-09-30_Neville_Chamberlaine_showing_the_Anlo-German_declaration_(%22Peace_for_our_time%22)._Heston_Aerodrome,_west_of_London,_England._Narodowe_Archiwum_Cyfrowe_3_1_0_5_268_3_1_111334_No_known_cop.jpg)
The folly of the Prime Minister's words became evident all too soon. In 1939, after Hitler invaded Poland, Chamberlain was obliged to tell his nation, with regard to Hitler,
His action shows convincingly that there is no chance of expecting that this man will ever give up his practice of using force to gain his will. He can only be stopped by force,
England was going to war.
The figures, both noble and ignoble, quoted below may have eventually changed their minds at some point, also. A speech, a phrase, by such a significant person, however, is preserved in amber. It has effect. In many cases, these statements were made when the person was quite mature, and had achieved stature.
I chose the quotes because to me they are representative of the author's place in history, of their world view, and of their character. My judgement on this is obviously subjective.
**The Characters**
- Franklin Roosevelt: President of the United States during the Great Depression and WWII. Helped to draft post-war world with Stalin and Churchill
Churchill, Roosevelt and Stalin at Yalta. _(B%26W).jpg)
Winston Churchill: Prime Minister of England during WWII. Largely credited with leading his nation to a hard-won victory against fascism.
Abraham Lincoln: President of United States during U. S. Civil War. Often rated by historians as the best president in U.S. history. Sometimes that honor is given to George Washington. Assassinated.
John F. Kennedy: President of United States for a short time in the 1960s. Remembered for his youth, his inspirational leadership, his brinkmanship with the USSR. Assassinated.
Donald J. Trump: 45th and 47th (current) President of the United States
Trump, by Miley Riley. White House Official Portrait. 
Dwight D. Eisenhower: Supreme Allied Commander of the Allied Expeditionary Force during World War II. Led the amphibious landing on Normandy at the end of the war. President of the United States in the 1950s.
George Washington: General who led army to victory during U. S. war for independence. First President of the United States.
Napoleon Bonaparte: Marched across Europe as the head of the French army. Became Emperor of France. Was eventually exiled and died in exile.
Joseph Stalin: Leader of the Soviet Union from the 20's until his death in 1953. Led USSR to victory in WWII. Sat down with Churchill and Roosevelt at Yalta. Together the three men divided up Europe--East and West. Soviet Bloc and Western-allied nations.
Adam Smith: Eighteenth-century economist/philosopher. Considered by some to be the father of modern capitalism.
Statue of Adam Smith by William Theed the Younger.
Nicholas II: Last Romanov Czar of Russia. Assassinated, along with his family, during the Russian Revolution of 1917.
John Adams: A leader of the American Revolution. Second President, first Vice president of the United States. Drafted Constitution for Massachusetts. One of the Founding Fathers of the United States.
Benito Mussolini: Fascist leader in Italy. Rose to power in the twenties. Became allied with Adolf Hitler in WW II. Was killed by a mob as the war came to an end.
Mussolini by Antola Swan. 1939. 
- Jimmy Carter: President of the United States from 1977 to 1981. Gained international renown after his presidency for his humanitarian work.
**Quotes**
The only thing we have to fear is fear itself.Franklin Roosevelt
An iron curtain has descended across the continentWinston Churchill
This was their finest hourWinston Churchill
A date that will live in infamyFranklin Roosevelt
A house divided against itself cannot stand.Abraham Lincoln--Paraphrasing
the Bible
Ask not what your country can do for you--ask what you can do for your country.John F. Kennedy
I am your justice...I am your retributionDonald J. Trump
...we must guard against the acquisition of unwarranted influence, whether sought or unsought, by the military industrial complex.Dwight D. Eisenhower
...the freedom of Speech may be taken away, and, dumb and silent we may be led, like sheep, to the Slaughter.George Washington
A Massive Fraud of this type and magnitude allows for the termination of all rules, regulations, and articles, even those found in the Constitution...Donald J. Trump
Change based on principle is progress. Constant change without principle becomes chaos.Dwight Eisenhower
In politics stupidity is not a handicap.Napoleon Bonaparte
Education is a weapon, whose effect depends on who holds it in his hands and at whom it is aimed.Joseph Stalin
Whenever the legislature attempts to regulate the differences between masters and their workmen, its counsellors are always the masters.
Adam Smith
...we will continue to deport these monsters...Donald J. Trump
Civil government, so far as it is instituted for the security of property, is in reality instituted for the defence of the rich against the poor, or of those who have some property against those who have none at all.Adam Smith
I shall never, under any circumstances, agree to a representative form of government because I consider it harmful to the people whom God has entrusted to my care.Nicholas II
He who saves his Country does not violate any Law.Donald J. Trump
The very definition of a Republic, is an Empire of Laws, and not of Men....John Adams
For Fascism the State is absolute, individuals and groups relative.Benito Mussolini
"When somebody is the president of the United States, the authority is total. And that's the way it's got to be. It's total.Donald J. Trump
...a question arises whether all the powers of government, legislative, executive, and judicial, shall be left in this body? I think a people cannot be long free...John Adams
“Our American values are not luxuries, but necessities — not the salt in our bread but the bread itself. Our common vision of a free and just society is our greatest source of cohesion at home and strength abroad — greater even than the bounty of our material blessings.Jimmy Carter
Every moment in time is a moment in history. Some moments, though, stand out as critical junctures. The development of the bomb may have been inevitable, but it was nonetheless a critical juncture. The same may be said of Kennedy's 1962 confrontation with Khrushchev over
missiles in Cuba.
It is my sense, and the belief of many people, that the United States is at a critical juncture. I try to understand what is happening by looking back at history. I try to gain perspective on the leadership in my country today. I hope some of my readers find this collection of quotes useful in the same way.
Thank you for reading. Peace and health to all.