take a/the bullet (for someone)
1. Literally, to jump in front of and absorb the impact of a bullet from a gun being fired at someone else. It's one of the basic duties of bodyguards to take the bullet for their clients if someone tries to kill them.
2. By extension, to accept or put oneself in the way of some misfortune, difficulty, blame, or danger as a means of protecting someone else. I don't know why you always feel like you have to take the bullet for your bosses when they screw up. They never reward your loyalty in any way. I used to take a lot of bullets when I worked as a PR representative for the senator.