The book does not hit shelves until May 5, but already the Republican Rand Paul has called its findings “big news” that will “shock people” and make voters “question” the candidacy of Hillary Rodham Clinton.

“Clinton Cash: The Untold Story of How and Why Foreign Governments and Businesses Helped Make Bill and Hillary Rich,” by Peter Schweizer — a 186-page investigation of donations made to the Clinton Foundation by foreign entities — is proving the most anticipated and feared book of a presidential cycle still in its infancy.

The book, a copy of which was obtained by The New York Times, asserts that foreign entities who made payments to the Clinton Foundation and to Mr. Clinton through high speaking fees received favors from Mrs. Clinton’s State Department in return.