Trump’s close associates — all of whom spoke anonymously with CNN to share his private thinking — said his preoccupation with Bush has been years in the making. His grievances, they said, go beyond policy disagreements with Bush over issues like the Iraq War, immigration and Common Core.

Described by friends as intensely competitive, Trump has a deep aversion to the idea of a dynasty candidate who might feel entitled to the party’s nomination. Privately and publicly, Trump is known to refer to Bush as “a stiff,” believing that the country badly needs a candidate who can energize the base and that Bush simply “is not a cheerleader,” one person in Trump’s inner circle said.

“For some reason they didn’t hit it off. Their styles are totally different,” one Trump friend said.

Trump’s animosity towards Bush in 2015 may come as a surprise to those who remember that years ago, the two men seemed to enjoy a friendlier relationship.