This move is not as much about Lehner as it is about giving Bishop a shot. When Murray made the move prior to the deadline, he explained that both Lehner and Bishop would be given a chance to prove themselves.
Lehner played well in his audition, now it's up to Bishop to show he can play at the NHL level. With Craig Anderson not expected back any time soon, the Sens will need contributions from both young goaltenders.
Bishop has looked good in Bingo, putting up a 2-1-0 record and a .944 save percentage.