Bullard said he has so far been willing to look beyond a slip in expectations as likely passing, and tied to oil price declines that are likely to reverse.

"Now we are 18 months into this and I am starting to wonder if my story is the right one," Bullard said. "For me inflation expectations are a key factor and if they continue to decline I would put increasing weight on that."

(Reporting by Howard Schneider; Editing by Andrea Ricci)