Which president has been elected once, voted out of office, and then back in.

Grover Cleveland

Explanation:

The First Democrat elected after the Civil War, Grover Cleveland was the only President that left the White House and then returned for a second term four years later. He was the 22nd and 24th President who was the only President to leave the White House and return for a second term four years later (1885-1889 and 1893-1897).

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