In the “Burn Like Napalm” mission, you’ll have to fray the rope. This has to be done as fast as possible because Lincoln will be burned alive if it isn’t.
In order to fray the rope, you must press WASD keys in quick succession. This will weaken the rope, however if you don’t do it fast enough the mission will be over. Once you’re done with the rope, you’ll have to quickly press Q to kill your target.