This chart shows the dominant long term trend in the US economy - gradual deceleration. A 20 year moving average is used to eliminate all cyclical or short term trends. The deceleration from 4.4% in 1969, to 4.1% in 1978, to 3.5% in 2002, to 2.5% in the first quarter of 2014 is clear. The temporary recovery in the late 1990s and beginning of the 21st century proved unsustainable and was followed by a sharper fall.
This trend shows that the most enduring feature of the US economy, which must be explained by any analysis, is not any analyses of business cycles, particularly those of a 'manic-depressive' type, but this very long term slowdown of the US economy.
Furthermore, as this deceleration has been going on for 40 years, it clearly has extremely deep roots which are very difficult to reverse. Unless dramatic changes in US economic policy take place, therefore slow deceleration should be built into projections for the US economy.