Three idioms for the price of one:)
1. A GAME OF CHICKEN is a conflict situation in which each side raises the danger level, hoping that the other side will be afraid and back down.
eg. This game of chicken can now only be resolved in one of three possible ways.
2. A SMOKING GUN is clear evidence of a crime.
eg. The search for other kinds of evidence tying him to trafficking has not produced a smoking gun.
3. If something is HANGING BY A THREAD, it is to be in great danger. You can also say hang by a hair.
eg. His life now hangs by a thread.