yes
James Buchanan was the U.S. Foreign Minister to Great Britain when he was running for President in 1856. Also, at least four Presidential candidates were former Ambassadors at the time they ran. The most recent is former U.S. Ambassador to the U.N. George H. W. Bush.
US President William McKinley
The president of the united states of America.
The US senate has to confirm the president's choices for ambassador.
George H. W. Bush was the tenth US Ambassador to the UN.
Yes a former US President can run for office of Vice President of the United States. A former US President can run and be elected for any other type of office.
The President.
Mohamed Tawfik is the Ambassador to the US for Egypt.
Eklil Ahmad Hakimi is the Ambassador to the US for Afghanistan.
Josko Paro is the Ambassador to the US for Croatia.
Tatoul Markarian is the Ambassador to the US for Armenia.
Josephus Daniels was sent by President Roosevelt to serve as an ambassador between the US and Mexico.
Hans Peter Manz is the Ambassador to the US for Austria.