Reagan's reputation

As many people have noticed, the Republican candidates for president have praised Ronald Reagan and said very little about other Republican presidents, even popular ones (it's a long time since I heard anyone claim to be an "Eisenhower Republican").  Even Democrats, notably Barack Obama, have said some positive things about him in recent years.  When did this start?  A number of surveys, mostly Gallup, have asked "How do you think Ronald Reagan will go down in history--as an outstanding president, above average, average, below average, or poor?"  (have did not mention "average" as an option but allowed people to volunteer it, and one asked for a rating of his "leadership" qualities, but there was no evidence that these differences affected the responses).  Here is a figure showing his average score, using +2.....-2 for the different responses.  

 

 His low point was July 1987, when he was under criticism for a variety of reasons, especially the Iran-Contra affair (on July 13, 1987 the New York Times ran a story entitled "GOP Hopefuls Backing Away from Reagan,' which makes interesting reading today).  His reputation had bounced back by the time he left office, and unfortunately there was a four-year gap before it was asked again.  At that time, he was almost back to his 1987 low, but since then it's been steady improvement:  each of the last four times it's been asked, he's set a new high.  I wonder if that's a common pattern, or something unique to Reagan.