In his emotional seven-minute farewell to a Republican Party that elevated his father and brother to the White House, there were two words that a choked-up Jeb Bush could not bring himself to utter: “Donald Trump.”

Mr. Bush, the former governor of Florida, had been soundly rejected by an electorate he no longer recognized, hobbling his campaign and leaving him little choice but to withdraw from the presidential race.

“The people of Iowa and New Hampshire and South Carolina have spoken,” Mr. Bush said, holding back tears. “And I really respect their decision.”

It was a stunning turn for the man who a year ago embodied all the qualities that his party’s elders imagined Republican voters wanted in a president: civility, experience, pedigree and tolerance.