Mr. President is the normal title used. Sir is appropriate, as in Yes, Sir and No, Sir.
Mr. President
how would u address a letter to the president of the u.s
In the United States in 1962, the US president was John F. Kennedy. He would address the Senate or the House if there was a cause to do so and by the Constitution, the president is obligated to address the whole Congress for an annual State of the Nation Address.
"Mr. President" is the proper address for the US President. "Mr. Obama" would probably not offend him.
president clinton
No
1600 Pennsylvania Ave, Washington DC
Nixon
By Act of Congress (Not the US Constitution) the President's letter of resignation goes to the US Secretary of State.
Harry Truman was President when the H-bomb was invented after his January state of the union address. Eisenhower did not mention it in his first 1953 address.
The White House - Washington, D.C.
On Saturday....