When they have a GOP president that isn't consider a failure historically.
You think George HW Bush's Presidency was a failure? I don't think so. He is generally well liked by both parties now. I would give him an "incomplete" on his presidency. His defeat was moderately because of the pop culture change in 1992 from the 1980's pop culture as to why he lost as President in 1992. Pop Culture really hasn't seen a backlash of a decade since the decade of the 80's got backlashed either. George HW Bush was at the wrong place at the wrong time partly and he really didn't have a plan for a second term to reduce the deficit and an economic policy which Clinton kind of did.
Now yes George W. Bush's presidency is viewed as a failure.