On Sunday, Mrs. Clinton will appear at the 37th annual Iowa steak fry hosted by Senator Tom Harkin; it will be her most overtly political appearance since resigning as secretary of state in February of last year.

Meanwhile, the largest Democratic fund-raising group, Priorities USA, which helped get President Obama elected, recently rebranded itself as a vehicle to help Mrs. Clinton. Publicly, the group says it is focused on raising money for Democrats for this fall’s congressional elections, but privately, Priorities has already started reaching out to donors to secure 2016 commitments for Mrs. Clinton.

“It’s very obvious what’s she going to do,” said Sue Dvorsky, a former chairwoman of the Iowa Democratic Party. “Clearly she’s going to run.”