New Jersey Gov. Chris Christie (R)  (John Gress/ Reuters)

To hear New Jersey Gov. Chris Christie (R) tell it, his gift to Mitt Romney wasn't his decision not to run for president in 2012. It was what he did next.

The gregarious and outspoken governor viewed his endorsement of Romney a week after announcing he would not run as the more notable prize, according to a forthcoming book by The Washington Post's Dan Balz.

Balz writes that toward the end of a fall 2012 interview with Christie, he asked whether the governor viewed his decision not to run "as a gift" to Romney. Christie replied, "The enormous gift was the next week," a reference to his endorsement of Romney. "For me to make that decision that quickly and to be willing to put myself out there for him that early, when no one else really had, I think was a real leap of a faith and a gift politically because nobody else was willing to do it," continued Christie, who added, "I wouldn't have used the word 'gift,' but since you did it seems to fit, it seems appropriate."

Christie said that when he told Romney he didn't have to do anything more to win his support, "He got this shocked look on his face and he turned to Ann [Romney] almost as validation that his ears had worked right." Romney, Christie said, later added, "Wow, Christmas in October."

Ann Romney then told Christie, according to the New Jersey governor's account, "Governor, you don't know how important and big this is." Christie responded, "I do."

Before he threw his support to Romney, Christie had warned candidates against raising money in the Garden State, leading to, in Christie's words, a "rather tense conversation" between himself and the eventual GOP nominee months earlier.

The book, titled "Collision 2012: Obama vs. Romney and the Future of Elections in America," is due out Aug. 6. It covers the 2012 campaign and its aftermath.

Christie's decision to support Romney came after he was courted by a parade of high-profile Republicans hoping to woo him into the race, including former secretary of state Henry Kissinger and conservative billionaire David Koch.

New Yorker Ken Langone once invited Christie to a breakfast, the governor recalled. Christie estimated that 60 people were in attendance at what he says he was led to believe would be a more intimate gathering.

Christie also recalled to Balz how former first lady Nancy Reagan ribbed him before a speech at the Ronald Reagan Presidential Library in 2011. Christie played along, seeming to enjoy her faux attempts to make him nervous.

"She turned to me and said, 'Do you know this is the second most press credentials ever asked for a museum speech, except for when President Bush 43 came here to speak?'" Christie told Balz. "I said, 'No, I wasn't aware of that either.' She goes, 'Hmmm, a lot of excitement tonight, do you have a good speech?' I said 'I think so.' She says, 'It better be.' "

Later, the former first lady informed Christie that he would be speaking at a podium former president Reagan had used. "I said 'Really?' " responded Christie. "She goes, 'Uh-huh.' I sat there for a second and I just turned to her and I said, 'You're bad, you know that?' She had this big smile on her face. She knew exactly what she was doing."