Republican presidential hopeful Ted Cruz and Karl Rove, the political strategists known as the "architect" of George W. Bush's gubernatorial and presidential campaigns, are engaged in an "epic feud" over an endorsement by Bush's father, former President George H.W. Bush.

The Texas senator claimed in his new book that Rove "suggested that the elder Bush was too old to have any good judgment anymore" after Cruz, who at the time was running for Texas attorney general, told the strategist that he had secured the former president's support.

The book, "A Time for Truth: Reigniting the Promise of America," is set to come out this Tuesday. In the book, Cruz also claimed that Rove threatened him, saying former President George W. Bush would "endorse my opponent and come out publicly for him" if the then-candidate dared to publicly mention a $1,000 donation he had received from Bush's father, George H.W. Bush, the Washington Post detailed.

The elder Bush's endorsement and contribution concerned Rove because many potential donors for George W. Bush's presidential library at the time were supporting Cruz's opponent -- and Rove was in charge of raising funds for the project, the Texas senator alleged.

But Rove disputes that assertion, insisting that his hesitation about Cruz's candidacy was due to incumbent Attorney General Greg Abbott not having ruled out a run for re-election.

"This put President George H.W. Bush potentially in the position of opposing a sitting officeholder who had previously been appointed to the Texas Supreme Court by his son, then-Governor George W. Bush," Rove explained in a Sunday post on Medium.

Rove added, "(And) my call to Mr. Cruz apparently didn't offend him back then because he continued seeking my counsel about his political ambitions, specifically his 2012 bid for the U.S. Senate."

Also on Sunday, Cruz, for his part, published an email written by Rove that said, "People raising money for the (presidential) library who are also (supporters of Cruz's opponent) will not understand why one part of the Bush family is for (another candidate)," according to the Dallas Morning News.

In a campaign statement accompanying the release, the presidential candidate upped the ante by accusing Rove of having published a "straight-out falsehood," saying his behavior was "why people are so cynical about politics."