Which of the following causes failure of coaxial cables?

Coaxial cable relies on a specific physical geometry and a clean, dry dielectric (insulator) between the center conductor and the outer shield to function properly. If moisture gets inside the cable, it changes the electrical properties of the dielectric, increasing signal loss and altering the cable's impedance. Over time, water intrusion will also cause the copper braid and center conductor to corrode or oxidize, completely ruining the cable's ability to carry RF signals efficiently. While power fluctuations and high duty cycles are common in normal operation, they will not damage a properly rated cable, making moisture the undisputed primary killer of coax.