This week, 48 years later, Romney is walking into his own nominating convention as the Republican Party gathers in Tampa. But the story line has turned upside down. Mitt Romney isn’t the moderate voice seeking to rein in the extreme forces in the GOP; he has become, as he called himself earlier this year, a “severely conservative” man looking to win the complete trust of the dominant right of his party, the Goldwater wing of his day. It is as if winning requires purging a key element of his father’s political legacy. But an examination of the forces behind Romney’s striking shifts on key issues makes it clear it is much more than that.

Romney’s appearances at these two conventions are bookends of a sort, set on either side of a winding ideological path, framing questions that go to the heart of the Romney canon. Call it a reasoned and heartfelt evolution, as the candidate does, or flip-flopping and shape-shifting, as his opponents prefer to put it. The question is not whether Romney has changed his outlook over the years — he undeniably has — but why. It is an evolution that combines many elements of the Romney saga: the bonds and breaks between father and son; the question about whether he has core convictions; and his politically bloody fight with the party that finally is poised to anoint him as its leader.

For much of Romney’s political career, the effort to understand him has been seen as epilogue of his father’s quest, a redemption story in which the son strives to succeed where his father failed. Everything, it often seems, has built to this moment in Tampa, and the nomination and acclamation his father never gained.

“To see your father basically assaulted” at the 1964 convention, “had to strike a powerful chord in Romney. That had to be absorbed into his heart and soul,” said Robert Goldberg, a biographer of Barry Goldwater who also has closely followed Romney’s career. “The question is: Why doesn’t that stick? How he escaped — that is another story.”

So what happened? How and why did the moderate Romney seek to redefine himself? And what does that say about the nominee in waiting, and the legacy of the family that shaped him?

In the beginning, the Romneys were almost apolitical, or at least nonideological. The elder Romney got his first big break by being hired in Washington as an aide to a Massachusetts Democrat, Senator David Walsh, and favored problem-solving over politics. Before seeking public office himself, he said, “I am neither a Republican nor a Democrat.”

Only the necessity of declaring for one party or another when seeking the Michigan governorship in 1962 — discussed at a family meeting in which Mitt participated — led George to announce that he was joining the Republican Party.

Early on, Mitt watched at his father’s side as the Romney philosophy took root.

On the day that George Romney declared his candidacy for governor, Mitt was there, absorbing his father’s views. It was a scene witnessed by The Boston Globe’s editor at the time, Laurence L. Winship, who traveled to Detroit and wrote a front-page story about the announcement. It marked the first appearance of Mitt Romney in the Globe.

“Fourteen-year-old Mitt . . . watched with sharp eyes as Mr. Romney handled a barrage of questions,” Winship reported. The younger Romney heard his father’s defining remark: “Policies designed for the benefit of the dominating group bring harm and hardship for those who live outside the border of privileged circles.” The Romneys, of course, were among the most privileged in America, living in one of the nation’s wealthiest communities, Bloomfield Hills. George Romney was a rich man speaking up for those who were not; a white man speaking up for minorities. He was, in short, a moderate out of sync with his party’s increasingly rightward tilt.