That America created only 88,000 jobs in March, less than half the number anticipated, was jolting news, indicating the recovery that the White House has boasted about may not be at hand. But in that March jobs report, there was more disturbing news. While unemployment fell to 7.6 percent, the reason it fell is alarming. Half a million U.S. workers (495,000) disappeared from the labor force. They dropped out. They are no longer even looking for a job. Worse, this appears to be an inexorable trend. The participation rate of eligible workers in the United States has fallen to 63.3...