Why Is Fast Growth Getting Harder for the U.S.?

It used to be common for the US economy to post a quarter of 4% or faster real GDP growth. In the 1980s (1981-1990), there were 18 such quarters. In the 1990s (1991-2000), another 18 quarters. But in the 53 quarters since then, the US economy has generated only six three-month periods of 4% real GDP growth or faster, including just two during the Not-So-Great Recovery.