White was guilty as charged when some critics said he had a hero-worship thing going on with JFK. This attitude definitly had an impact on White's writing as his descriptions of Kennedy were some of the best pieces of political prose Ive ever read. Also, Nixon was not as testy with reporters at the time and thus White had better access to him in '60 then in '68 (though White presumabley had more time with Nixon in 1968 than the average writer). Both '60 and '68 were very dramatic campaigns/elections with intriguing storylines...albeit for different reasons. In my opinion, White's '68 book has a huge problem with his lack of understanding/empathy towards the youth/college/peace movement...this is exemplified by his use of the word 'youngsters' to basically discredit a large bloc of people in the pages leading up to his description of the Chicago riot. For better descriptions/analysis of the Chi riot see the American Melodrama book (with pretty good coverage by its Brittish authors) and Hunter S Thompson's '72 book (where he describes being assaulted in 1968 by the Daley Gestapo).
I highly reccomend you read the 1960 book, Y2Jerk.