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.
Eklil Ahmad Hakimi is the Ambassador to the US for Afghanistan.
Mohamed Tawfik is the Ambassador to the US for Egypt.
Tatoul Markarian is the Ambassador to the US for Armenia.
Josko Paro is the Ambassador to the US for Croatia.
Peter Taksoe-Jensen is the Ambassador to the US for Denmark.
Hans Peter Manz is the Ambassador to the US for Austria.