In 1978 the U.S. Mint began to significantly decrease the mintages to circulating Kennedy Half Dollars. For the 1978-P Kennedy Half Dollar, the Mint struck a little over 14 million examples. The previous year it struck over 40 million. And most years prior to that the Mint struck some dates in the hundreds of millions.
Most 1978-P Kennedy Half Dollars are common in MS65 condition or lower. In Ms66 condition you really have to search hard through Mint Sets or rolls to find them. In MS67 condition or higher they are very difficult to find.