The day before Florida’s 2016 presidential primary, the state attorney general, Pam Bondi, surprised her fellow Republicans and endorsed Donald J. Trump at a rally in Tampa, her hometown.

Her first choice, former Gov. Jeb Bush of Florida, had recently dropped out. Senator Marco Rubio, another Floridian, remained in the race, though just barely. Few big-name Republicans in the state, and none as high-ranking as Ms. Bondi, had yet backed Mr. Trump.

In him, Ms. Bondi saw a bit of herself: an outsider with no experience in elective office. She first won the state attorney general’s race in 2010, during the Tea Party wave that catapulted novice Republican candidates like her into power.

By 2016, she was part of the state’s political establishment. But the party, she saw, was on the cusp of another pivotal moment — and her foresight then is responsible now for Mr. Trump’s decision to pick her to lead the Justice Department, as U.S. attorney general.

“Something that you don’t forget is when someone comes and gets behind you early in a situation when it’s not popular,” said Adam Goodman, a Tampa political consultant who has advised Ms. Bondi since recruiting her to run in 2010.

Over the last eight years, as Florida became Mr. Trump’s home, a cradle of right-wing politics and a solidly Republican state, Ms. Bondi went from being a traditional Republican to a Trump loyalist. Acting as confidante, impeachment lawyer and adviser, she ascended in the president-elect’s inner circle thanks to the combination of charm, savvy and a light touch that characterized her career as a telegenic prosecutor and a politician.