The phrase 'down to the wire' is something we use commonly nowadays to denote tense finishes and endings. Though this term is used to denote any situation that has a very tense ending, with uncertainty being the predominant factor till the last instant, the term is used more commonly in sporting events. It is the phrasal equivalent of the modern day 'photo finish', though the former term has been in use much longer than the much more recent 'photo finish.'
The use of the phrase originated in the sport of horse racing. In the early days, the finish line for horse races had a wire that stretched across the track, from one end to the other, much like the ribbon or tape we see nowadays in races and sprints. The purpose of this wire was to determine which horse crossed the finish line first. Sometimes two or three horses seemed to cross the finish line at the same time. Since horse racing involved money, it became prudent to declare one winner, not two or three joint winner. This was done by carefully observing which horse's nose had nudged this wire. The horse that touched the wire first was declared the winner. That is how the phrase 'down to the wire' originated – to denote a situation where a horse was declared a winner by determining which of them had hit the wire first.
The use of the phrase originated in the sport of horse racing. In the early days, the finish line for horse races had a wire that stretched across the track, from one end to the other, much like the ribbon or tape we see nowadays in races and sprints. The purpose of this wire was to determine which horse crossed the finish line first. Sometimes two or three horses seemed to cross the finish line at the same time. Since horse racing involved money, it became prudent to declare one winner, not two or three joint winner. This was done by carefully observing which horse's nose had nudged this wire. The horse that touched the wire first was declared the winner. That is how the phrase 'down to the wire' originated – to denote a situation where a horse was declared a winner by determining which of them had hit the wire first.