what does "He was Sammy Glick in Sammy's graduation photograph"mean?
This was the first time Larry had seen Jack since yesterday's wind-up conference in Houston before the testimonial dinner for Albert Thomas. He was the same Valenti —alert, intent, straining for some unseen bait—but there was a new zeal about him. He was Sammy Glick in Sammy's graduation photograph, and O'Brien, noticing the throbbing veins in his neck, thought, Well, he's on his way now. Muggsy O'Leary saw Valenti, too. At the same time it occurred to Muggsy that there had never been so many Texans in the stateroom. • He thought, It's all over for us.

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Sammy Glick was the name of a fictional character in the 1941 book 'What Makes Sammy Run'.  In the book, Sammy Glick was smart and ruthless, savvy and crude.  He would do anything to claw his way up the ladder of success. 
The name Sammy Glick became synonymous with coldblooded ambition.  In this paragraph, Larry O'Brian was comparing Jack Valenti to the Glick character(a negative comparison), as he noticed a new zeal(excitement) in Valenti as he watched him.  He could see that Valenti was the type of person who would do whatever was needed in order to gain some position in the Johnson administration.  "Well he is on way now" means that O'Brien could already see Valenti trying to gain favor with Johnson and Johnson' staff.  The graduation photo comment means that if you wanted to visualize how the Glick character might look , all you would have to do is visualize Valenti's photo.