“She told us that we were ready to sail the ship, that we did not need her there, and that we would be able to do it on our own,” said Patricia McCoy, a Boston College law professor who was a senior official at the bureau.

Ms. Warren was right. Under her successor, Richard A. Cordray, the bureau would recover $12 billion for consumers from financial institutions by 2017. It would become, to supporters, a prized example of the government taking on big banks after the 2008 financial crisis. To opponents — Republican lawmakers, business associations and a few conservative Democrats — it would become an example of “runaway government,” an agency to be curbed at the first opportunity.

To Ms. Warren, the bureau is something else as well: a formative lesson in how an idea — a plan — can become reality. For it was through creating a new financial regulator that Ms. Warren developed the approach to government that now guides her presidential campaign. And it was in losing the chance to lead her bureau that Ms. Warren came to see the value of asking voters, rather than a president, to give her power.

A review of Ms. Warren’s role in creating the consumer bureau, including interviews with more than 30 people involved in the process, revealed an approach to politics that joins imaginative policy ideas with a keen instinct for mass communication and a willingness to negotiate. On one hand, she marshaled support from progressive activists and helped build public demand for her idea; on the other, she haggled with members of Congress to earn their backing.

David Axelrod, who was Mr. Obama’s top political adviser during the battle to create the C.F.P.B., called Ms. Warren’s role a “bona fide credential” for the presidency.