Robert Rubin has moved seamlessly between Wall Street and Washington. After making his millions as a trader and an executive at Goldman Sachs, he joined the Clinton administration.

But while Mr. Rubin certainly did not have direct responsibility for a Citigroup unit, he was an architect of the bank’s strategy.

Former colleagues said Mr. Rubin also encouraged Mr. Prince to broaden the bank’s appetite for risk, provided that it also upgraded oversight — though the Federal Reserve later would conclude that the bank’s oversight remained inadequate.

Once the strategy was outlined, Mr. Rubin helped Mr. Prince gain the board’s confidence that it would work.

Citigroup insiders and analysts say that Mr. Prince and Mr. Rubin played pivotal roles in the bank’s current woes, by drafting and blessing a strategy that involved taking greater trading risks to expand its business and reap higher profits. Mr. Prince and Mr. Rubin both declined to comment for this article.