The most common and most likely answer to this crossword clue is the 15 letter word PRESIDENT-ELECT
I've seen this crossword clue in The Times
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More clues leading to the result PRESIDENT-ELECT
Buddy explains!
The straight part
We know that "individual heading for office" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case individual heading for office = president-elect.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does PRESIDENT-ELECT mean?
PRESIDENT-ELECT noun- (sum of parts) A person who has been elected to a presidency but has not yet been inducted into office.