Hillary Clinton and Sen. Claire McCaskill once had such hate the Missouri Democrat said she feared being in an elevator with the former first lady, a book says. "I really don't want to be in an elevator alone with her," McCaskill told a friend in remarks quoted in the forthcoming "HRC: State Secrets and the Rebirth of Hillary Clinton." The tension between the two Democrats came after McCaskill said on NBC's "Meet the Press" while she was running for election that former President Bill Clinton was "a great leader, but I don't want my daughter near him," authors Jonathan Allen of Politico and Amie Parnes of the Hill say in the 448-page book, to be published Feb. 11. McCaskill instantly regretted the remark, the book says. Indeed, the unfiltered comment brought her "to the point of epic tears," the book quotes a McCaskill friend as saying. The remark prompted Hillary Clinton to immediately cancel a planned fundraiser for McCaskill, the book says. McCaskill phoned Bill Clinton a few days later to give a tearful apology, and his gracious response only deepened her distress, the book says. In 2007, when Hillary Clinton, then a U.S. senator from New York, started her unsuccessful White House run, she sought to mend fences with McCaskill at a private lunch in the Senate dining room, where the two spoke about campaigning's physical rigors. But the bonding attempt didn't stop McCaskill from endorsing Sen. Barack Obama, D-Ill., for president in January 2008. She also successfully proposed to the Obama campaign two other prominent female Democrats should come forward during the same period -- Kansas Gov. Kathleen Sebelius, now secretary of health and human services, and Arizona Gov. Janet Napolitano, who later became homeland security secretary before stepping down in September to lead the University of California system. McCaskill, 60, who chairs the Senate homeland security ad hoc panel on contracting oversight, has recently worked hard to improve relations with 66-year-old Hillary Clinton -- most conspicuously with her June 2013 endorsement of Clinton for president in 2016. "Now, as I look at 2016 and think about who is best to lead this country forward, I'm proud to announce that I am Ready for Hillary," McCaskill said a statement posted at ReadyforHillary.com.