The number cited is the black line in the chart to the left.
The more realistic number is the gray line, which includes part-timers, and the unemployed.
If you want to know what's the plight of 25-64 year old (i.e. fit to work) men in the States over time, looking at the black line is like judging a fruit vendor by looking at the fruits displayed on top of the pile.
Removing part-timers and the unemployed is naughty because those are precisely the ones who would drag down the average. This is clearly shown in the chart, where the gray line is everywhere beneath the black line.
The other feature of interest in this analysis is the "plummeting" of the median. The median is the mid-point of a distribution: half the men earn above that amount, and half earn below that the median earnings. It is not a number that is easy to manipulate (especially when the data have been adjusted for inflation).
If someone who's earning $25K (below median) becomes unemployed, this event has no impact on the median because earning $0 also is a below-median number. To move the number down significantly, we need big shifts from above-median to below-median.
Let's pick out 1997 when the median earnings of all men peaked at about $40,000. The median then declined over the next 10 years or so to $33,000 or so. This means that instead of 50% earning less than $40K, we now have a higher than 50% of men earning less than $40K. This keeps getting worse over time. One percentage point represents 800,000 people as there are some 80 million men between 25 and 64.
The fact that the full-time median has stayed flat implies that it's the bottom that has fallen out. (There is an additional chart cited by Klein that showed that the average full-time earnings have soared in the same period, and that is possible because the median would not move if we suddenly doubled the earnings of the top 1%; such a policy would result in a drastic increase in the average earnings.)
When the median number is changing as drastically as is portrayed here, we are looking at a crisis.