In the clearest signal yet that he is actively considering a run for president in 2016, Vice President Biden will headline Iowa Sen. Tom Harkin's annual steak fry next month, according to sources briefed on the event.

Joe Biden, left, is going to Iowa.

"The vice president accepted Senator Harkin's invitation to attend the steak fry this year," said a source in the vice president's office. "It has been a long-standing commitment after the vice president was unable to attend last year."