The Interdecadal Pacific Oscillation (IPO), in a negative phase with below-normal tropical Pacific SSTs on average since 2000, appeared to undergo a transition from negative to positive triggered by the 2015-2016 El Niño event.  However, in early 2020 a La Niña event was initiated and lasted for three years.   Though multi-year La Niña events are not unprecedented, the onset of this event corresponded to the huge amounts of smoke produced by the disastrous 2019-2020 Australian bushfires, and here we examine processes that prolonged the event to a third year.  Multi-year climate model hindcasts with E3SM2 and CESM2 initialized in August 2019, both with and without the effects of bushfire smoke, confirm earlier results that the smoke traveled across the Pacific to South America where it brightened the clouds and produced cooler SSTs that were then advected northward to the equatorial eastern Pacific, thus producing La Niña conditions in the first year.  Once established, Bjerknes feedbacks maintained the La Niña long after the effects of the smoke dissipated.  SST, precipitation, convective heating, wind stress, and resulting off-equatorial ocean heat content anomalies in the western Pacific contributed to maintaining these conditions into a third year.  These coupled processes over three years have implications for how a negative phase of the IPO could be maintained for multiple years.