I'm looking for the title/author of a sci-fi book I read in the mid 90's but was probably at least 5-10 years older than that.

The basic premise was of a older guy who as an amateur scientist had discovered that the Earth's magnetic field changed orientation every few thousand years, and was currently long overdue. One of the main things I can remember is that early on in the book he used an attempted assassination of the US President (using wax bullets instead of the real thing), in an attempt to get the attention of the authorities.

There was a lot of other stuff about how this would explain the myths of Atlantis and the Egyptians & Mayans having such advanced technologies. In the end people bought into his theory, but we only just getting prepared when the lights went out...

Any ideas?

Thanks.