When a Triple Crown is on the line in the Belmont Stakes, the race boils down to one essential question: Will he or won’t he? That’s certainly the case this year, when Justify will arrive in New York without any obvious rival for 3-year-old thoroughbred supremacy. The Kentucky Derby and Preakness champion could face as many as 10 challengers on June 9, most of them far better rested than he. But the more pressing opponents are his own potential limitations and the inherent difficulty of the Triple Crown. Though American Pharoah made it look relatively easy three years ago, the 37 years of futility that preceded him taught us the 5-week test is, in fact, maddeningly hard. So many excellent horses tried and failed for reasons of competition, health, stamina and luck. Will one of those factors topple Justify or will he become the 13th horse in history good enough to trample all questions? Here are five storylines to watch as we look forward to his attempt. For perhaps the first time in his three-month blitz on the sport, Justify looked worn out as he approached the wire at Pimlico Race Course. Jockey Mike Smith said he eased him up slightly, because he was confident the victory was in hand. But by almost any measure, Justify’s performance in Baltimore was a step back from his 2½-length victory in the Derby. As rival trainer Chad Brown noted the day before the Preakness, it’s extremely difficult for any young horse, even a great one, to improve race after race. And Justify had already come so far since his maiden start on Feb.18. Not to mention, he had to run on a mud-caked track for the second time in two weeks. All of those factors might have kept him from showing his best. And he still won — the mark of an excellent horse and potentially a classic one. But what does it mean going forward? Trainer Bob Baffert has said he expects Justify to rebound with a big effort at Belmont. The massive chestnut looked terrific the morning after the Preakness, and he breezed half a mile in a striking 46.8 seconds on Tuesday morning at Churchill Downs. On the other hand, Hall of Fame jockey Jerry Bailey and others have noted that the best horses often fool us by looking sensational in training. They’re so talented and professional that we can’t see how tired they are until they have to dig deep in a big race. The 1 ½-mile Belmont could certainly offer Justify that kind of test. The history of Belmont runners coming off tired efforts in the Preakness is poor. But the best horses, the Triple Crown winners, turn history on its head. The beauty is that we probably won’t know until midway through the race on Saturday evening. Probably not. He wins the resume race in this field by more lengths than he won the Derby. We have the usual array of returning challengers from the Derby, including seventh-place finisher Hofburg, who closed well despite a difficult trip at Churchill Downs, and Wood Memorial winner Vino Rosso, whose owners feel he’s built for distance. Tenfold made up significant ground on a tired Justify in the stretch of the Preakness, and his Hall of Fame trainer, Steve Asmussen, seemed eager for a rematch. Bravazo ran gamely in both the Derby and Preakness, where he finished a close second. But his trainer, D. Wayne Lukas, calls Justify the King Kong of this class. The 82-year-old Lukas always says you have to show up and run in case the big guy falters. And that’s essentially the story for each of the 10 potential challengers. This is probably a question for racing lovers more than casual sports fans, but it’s inevitable given that the Triple Crown aspirant is owned by the exact group that owns his would-be top challenger. In announcing that Audible would not run, trainer Todd Pletcher said his horse was not doing as well as he had been in the run-up to the Derby and that he preferred to freshen him for the summer. But skeptics will say the ownership group, led by WinStar Farm, wanted to clear the way for Justify to win the Triple Crown and reap the financial rewards associated with it. From a business standpoint, such a call would be understandable. From a pure sports standpoint, Audible’s absence is a bummer. He came into the Derby as highly touted as Justify, and after initial difficulty handling the mud at Churchill Downs, ran as well as any horse over the second half of the race. He was the lone potential Belmont challenger who seemed a genuine threat to an on-his-form Justify. The Belmont always feels like a big event, live and on television, when a Triple Crown is on the line. That will surely bear out in both attendance and television ratings. That said, there’s no way to replicate 37 years of anticipation — the agony of near-misses, the hunger for a star to lift a struggling sport, the questions of whether a Triple Crown was too difficult in an age of lightly-raced horses— that set the backdrop for American Pharoah’s indelible run. In the 1970s, when three horses won the Triple Crown in five years after a 25-year drought, there was talk of fatigue with the achievement. Affirmed, despite his stirring rivalry with Alydar, was probably not as celebrated as Secretariat. None of this is Justify’s fault. If he pulls it off, we may come to view him and American Pharoah as a golden pair from the 2010s, just like we now see Secretariat, Seattle Slew and Affirmed as a set. But as an in-the-moment event, his Belmont run probably won’t carry the same historic tension as Pharoah’s victory. We saw the limits of this question with American Pharoah. His three races after the Triple Crown felt like festivals as casual fans flocked to celebrate a generational talent. But as industry analysts had warned, no one horse was going to reverse the business declines that have weakened racing in so many parts of the country. Justify certainly could be a star of the same ilk. Like Pharoah, he’s trained by the enduring face of the sport in Baffert. He’s undefeated. He’s a magnificent looking animal — about the same height as Pharoah but packing an extra 100 pounds of muscle. He approaches training and race days with calm dignity, despite the fact he’s still fairly new to all of this. The swiftness of Justify’s rise sets him apart from previous Triple Crown candidates. Even Baffert had not seen him run until January. As soon as he did, the Hall of Fame trainer knew he had another monster on his hands. He has compared Justify to LeBron James. Given the barriers he’s already smashed, this is a horse to remember even if he does not win at Belmont.