programming, operating system
Any error which causes abrupt termination of the program. The program may be terminated either by itself or by the operating system (a "fatal exception"). In the former instance, the program contains code which catches the error and, as a result, returns to the operating system or calls an operating system service to terminate the program.
He tanked with right-wing voters because he made the fatal error of showing some humanity to the children of illegal immigrants.
The fatal error was to do it through intelligence services, and in secret.