It doesn't seem to be getting harder to pass the bar in the U.S. In 2000, 72,704 bar examinations were taken, with 47,160 passing, ~65%. In 2013, 83,986 exams were taken, with 57,026 passing, ~68%. Those are the yearly totals, I guess they include people taking the exam twice.

I got the numbers here:

http://www.ncbex.org/publications/statistics/

I picked those 2 years just because, I didn't look at any other years.