Definitions for "front-runner"
Keywords:  runner, horse, far, tries, nominee
A horse whose running style is to attempt to get on or near the lead at the start of the race and to continue there as long as possible.
A front-runner is a horse that tries to lead the field as far as possible. When you have a race with a few front-runners, the race is prime for a closer to challenge for the win.
A horse who usually leads (or tries to lead) the field for as far as he can
a competitor thought to be most likely to win.
the candidate with the most news coverage
A candidate in any election or nomination process who is considered to be the most popular or likely to win.