For the 12 years that his father held national elective office, Mr. Bush used his unique access to the highest reaches of government to seek favors for Republican allies, push his views and burnish his political profile in his home state, a review of presidential library records shows. In the process, Mr. Bush carefully constructed an elaborate and enduring network of relationships in Florida that helped lead to his election as governor in 1998 and, now, to his place as a top contender for the Republican presidential nomination in 2016.

It was a period when Mr. Bush, a real estate developer and entrepreneur in his late 20s and 30s, made his debut in regional politics, parlaying his family name into the chairmanship of the Dade County Republican Party and emerging as a sought-after figure for anyone trying to reach the White House.

The letters from Mr. Bush kept at the George Bush and Ronald Reagan presidential libraries show him to be sometimes compassionate, occasionally demanding and always conscious of his status as a member of a prestigious and powerful political clan. He thought nothing of making requests big and small, but acknowledged an underlying anxiety about coming off as something very un-Bush-like: an overeager local party boss, “another bad breath county chairman,” as he wrote in a request to President Reagan.

Even within a family long steeped in politics, Mr. Bush stood out to White House aides for the frequency of his communications and the intensity of the opinions.