Former Rep. Ron Paul is warning in television commercials of a calamitous U.S. financial crisis that could bring civil unrest and a stock market collapse—a crash “infinitely worse than the crisis of 2008.’’ He urges viewers to prepare by buying a “Survival Blueprint,” a book of advice from an investment research firm.

The commercial is being broadcast nationally at a time when his son, Sen. Rand Paul of Kentucky is trying to build a more mainstream presidential campaign than those of his father, a libertarian who was regarded...