Mr. Vilsack once thought his smarts about Iowa could catapult him to the presidency. But his 2008 bid for the White House quickly fizzled, and he endorsed Mrs. Clinton.

His efforts to deliver his state for her failed when Mrs. Clinton ran into Mr. Obama’s Iowa juggernaut.

Now, Mr. Vilsack is heading into his final year at the Agriculture Department, where he helped negotiate the 2014 farm bill, a nearly $1 trillion measure that had sparked four years of partisan fighting over farm subsidies and support for the food stamp program for the poor.

Mr. Vilsack was also central in pushing for passage of the Healthy, Hunger-Free Kids Act in 2010.

The law mandated the use of whole grains, vegetables and fruits at schools and required that students select at least one portion of fruits or vegetables at every lunch.

He has also pushed for the use of biofuels. This past month, Mr. Vilsack joined Ray Mabus, the secretary of the Navy, as the guided-missile destroyer William P. Lawrence was filled with biofuel made from beef fat. He called it an “extraordinary experience” and said it is an example of the “series of partnerships that has extended the reach of the U.S.D.A.”

Mr. Vilsack is a low-key, soft-spoken man, and his job overseeing the nation’s farmers has largely kept him out of the spotlight. The exception came early in his second year in the job, in what he acknowledges was the low point in his career.

Reacting to a video that showed seemingly racist comments from Shirley Sherrod, an Agriculture Department official in Georgia, Mr. Vilsack quickly fired her. He was forced to publicly apologize to Ms. Sherrod days later when it became clear that the video had been heavily edited by the operators of a conservative website. In fact, the full video showed Ms. Sherrod offering a lesson in racial tolerance and compassion.