Claude A. Swanson (1862-1939), Virginia’s U.S. Senator from 1910-1933, had a rule for new Congressmen that was published in Current Opinion in 1923: “When in doubt, do right.” Swanson’s rule means that when in doubt between the success of doing the wrong thing (such as self interest) and doing the right thing for constituents, if things are equal or in doubt, the right thing should be done. It’s not known when Swanson first formulated the saying.
 
New York politician James A. Farley (1888-1976)—New York City’s James A. Farley Post Office was named in his honor—wrote in 1948: “More than once since, I have had occasion to recall Mark Twain’s famous line, ‘When in doubt, do the right thing.’” There is no evidence that Mark Twain (1835-1910) ever said this. “When in doubt, do the right thing” was said on the television political drama West Wing in 2006.
 
   
Wikipedia: Claude A. Swanson
Claude Augustus Swanson (March 31, 1862 – July 7, 1939) was an American lawyer and Democratic Party politician from Virginia.
 
He served seven terms in the U.S. House of Representatives, from 1893 until 1906, was the 45th Governor of Virginia from 1906 until 1910, and represented Virginia as a United States Senator from 1910 until 1933. Swanson lived most of his life at his estate Eldon in Pittsylvania County, Virginia, built by the Whittle family for whom Chatham’s Whittle Street is named.
 
He was Secretary of the Navy under Franklin D. Roosevelt from 1933 until his death at age 77.
     
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1 July 1923, Current Opinion, “The Colyumists’ Colyums,” pg. 104:
Among the visitors to Washington since Congress adjourned are many Congressmen-elect, installing themselves in the House Office Building and incidentally “learning the ropes.” One of them asked a veteran legislator for some pointers on how to make a success in Congress.
 
“I know of no better way,” was the reply, “than to follow the rules once laid down by Senator Swanson of Virginia to a bunch of new Congressmen:
 
“‘First. Work one day and then take six days off to talk about it.
 
“‘Second. Never take anything you can’t carry.
 
“‘Third. When in doubt, do right.
 
“‘Fourth. When the water rises to the second deck, put on a life preserver and follow the rats.’”
       
27 March 1927, Cleveland (OH) Plain Dealer, pg. 7A, col. 3:
Of Senator Claude A. Swanson of Virginia:
 
“Unlike Glass, Swanson is always suave, and he is a consummate politician. He is a born horse trader. He is reputed to live by three mottoes: ‘When in doubt, do right,’ ‘When the water reaches the upper deck, follow the rats’ and ‘Be bold as a lion on a rising tide.’
   
19 June 1927, Syracuse (NY) Herald, sec. 1, pg. 10, col. 7:
This story has to be anonymous. A great national politician was talking about the place of honesty in politics. “I’ve had a steady motto,” said he. “My rule is: When in doubt, do right.” Just repeat that “When in doubt, do right,” a few times and get its full beauty.
 
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Political Behavior:
The heretofore unwritten laws, customs and principles of politics as practiced in the United States
By Frank R. Kent
New York, NY: W. Morrow
1928
Pg. 153:
One, for example, is this — “When in Doubt, Do Right.”
 
4 September 1928, Syracuse (NY) Herald, pg. 8, col. 3:
The rules of political success as Mr. Kent sets them forth are: (...) “When the water reaches the upper decks, follow the rats”—which means abandon any principle you have when it becomes unpopular;...
 
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Confessions of a Congressman
By Jerry Voorhis
Garden City, NY: Doubleday
1948, ©1947
Pg. 232:
“When in doubt, do right.” This sage advice to young congressmen is credited to the late Claude A. Swanson, senator from Virginia and the first of President Roosevelt’s many Secretaries of the Navy.
 
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Jim Farley’s Story - The Roosevelt Years
By James A. Farley
New York, NY: Whittlesey House
1948
Pg. 290:
More than once since, I have had occasion to recall Mark Twain’s famous line, “When in doubt, do the right thing.”
   
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Counsel to the President:
A memoir
By Clark M. Clifford with Richard C. Holbrooke
New York, NY: Random House
1991
Pg. 580:
1 concluded my arguments in favor of a full bombing halt with one of President Truman’s favorite Mark Twain sayings: “When in doubt, do right. This will gratify some people and astonish the rest.”
   
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Basic Managerial Skills For All
Eighth edition
By E. H. McGrath
New Delhi: Prentice-Hall of India
2003 (?)
Pg. 819:
“When in doubt, do the right thing.” — DEAN ACHESON
   
West Wing Season Seven Quotes
Episode 714 Two Weeks Out
Original Airdate 03-19-06
“When in doubt do the right thing — the rest of the time get away with whatever you can.”
- Vinick, with an old aphorism