You can decompile a program down to "a" source. Not "its" source. It certainly won't be very readable, and that's assuming that only an optimizer was used in the compiler back-end. Consider if they use an obfuscator.

It's not impossible to deciper such things, but it's not easy at all. Since there's a lead time for this (say, from the software release date until the election), making it hard is enough.