Spectre, of course, has already had its opening weekend. It is a stretch to call a $73 million take in the first three days of release a flop. This may be all the more the case given the timing of its release. (Coming on the heels of The Martian and sharing an opening weekend with Peanuts, in a year already packed with spy movies, plausibly hurt it.) However, it is also less than a triumph given the series' history and the film's extraordinary cost (and a contrast with how well the movie is doing in just about every other market in the world).
Ironically, this may make the second weekend that much more important--how well it holds up indicating how far any "underperformance" will carry. In other words, while I myself expressed no expectation that the movie would have exceptional legs, it may still earn more than that first weekend suggested, and there is at least one reason to think so. As Gitesh Pandya noted, both prior Bond films faced much tougher competition in their second weekends than Spectre will. (Both those films went up against Twilight movies.)
For his part, Mr. Pandya anticipates a 50 percent drop--not at all bad for a big sequel like this, and this does not seem out of the question to me.
Just Out . . . (The Many Lives and Deaths of James Bond, 2nd edition)
My Posts on Spectre
Just Out. . . (James Bond's Evolution)
Too Many Spies?
Just Out . . . (The Forgotten James Bond)