A lot of blue collar manufacturing jobs have been exported overseas, with financial help from Uncle Sam who gives tax credits for destroying American jobs. 
There is also downward pressure on American workers from the millions of workers who are in the country illegally and so will work for far less.
globalization flatted wages and will continue to do so. ever since 1945, america has slowly lost its competitive advantage.
my salary has been frozen by the state. my state health insurance has also seen premium increases every year. it's the new reality.
D) All of the above are correct.
Bonus answer: Technology
The best way to deal with the illegals is to have a guest worker program like they do for the migrant workers who pick crops. That way you get to vetted them and they and the people who hire them have to pay income tax and social security taxes. After you implement the guest worker program you then make the penalty for comin here illegally and for hire illegal immigrants tougher.
Most of the competitive edge America lost is due to the high price of health care. Once you lower health care cost to the same cost as the European countries America is very competitive. We don't have to compete with third world countries with low cost manufacturing. We need to compete with the first world countries with high tech.
US blue collar men now compete with Vietnamese blue collar men who make a couple of dollars a day adjusted for inflation. Does the American consumer shop for the most expensive product? That is why progressives need to build need to open companies, hire many and pay high wages and benefits to stop this travesty, regardless of whether people buy the products are not, people will be working.
You had better watch out yourself, steamed. If the Vietnamese are good at anything it is creating propaganda.
You could find yourself either being replaced by one of them or you being paid with a small bag of rice per day.
stewartm0205
The real reason that blue collar workers make less is that fewer of them belong to unions.