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.

“We will see a pattern of financial transactions involving the Clintons that occurred contemporaneous with favorable U.S. policy decisions benefiting those providing the funds,” Mr. Schweizer writes.

His examples include a free-trade agreement in Colombia that benefited a major foundation donor’s natural resource investments in the South American nation, development projects in the aftermath of the Haitian earthquake in 2010, and more than $1 million in payments to Mr. Clinton by a Canadian bank and major shareholder in the Keystone XL oil pipeline around the time the project was being debated in the State Department…

Members of the Senate Foreign Relations Committee, which includes Mr. Paul and Senator Marco Rubio of Florida, have been briefed on the book’s findings, and its contents have already made their way into several of the Republican presidential candidates’ campaigns.