Sure, there’s always periodic swings, but overall the graph is heading steadily downward for xtians. Over 90% of US citizens identified as christians in the early 90’s. It’s now 63% and at the same time, atheists have risen from practically zero to nearly 30%.
Globally, the same pattern is seen and whilst they’ll always be periodic swings up and down, overall the global trend is still going down and there’s no real reason to suppose that will reverse.
Islam on the other hand, is growing. It’ll probably outstrip xtianity worldwide sometime in the next 25-30 years and atheism will probably decline overall as Islam increases.