within striking distance of being elected; in the running
Used in election contexts to describe a candidate who has a realistic chance of winning. Often appears in phrases like 当選圏内に入る or 当選圏内にいる.
He moved into the range of being electable in the opinion polls.
Candidates who are within striking distance make a final push.
当選 means 'being elected' or 'winning an election', while 当選圏内 refers to the state of being close enough to win.
圏内 means 'within a range or sphere'; 当選圏内 specifically applies this to the electoral context.
Compound of 当選 (election victory) and 圏内 (within a range). The exact historical derivation is uncertain, but the term is a straightforward modern political expression.