The author of a book that fueled an FBI investigation into the Clinton Foundation now is taking aim at two new targets—the families of Senate Majority Leader Mitch McConnell and former Vice President Joe Biden.

In a new book, “Secret Empires: How the American Political Class Hides Corruption and Enriches Family and Friends,” conservative author Peter Schweizer argues that China has worked to gain leverage over powerful American politicians by targeting their families with investment opportunities and business deals, providing...