I'll make a simple multiple choice question: LOL.
I'll try to make my answer as simple as possible; since you didn't get my simple analogy of more-criminals-in-prison = less crime.
Less than 10%.
Now, here's the part you don't get: Where did all the union jobs go?
Most went to other countries. Some companies closed and won't be replaced anytime soon.
Here are a couple of interesting links for you, if you care to do some homework on the subject:
“A huge part of the union membership loss can be traced to the jobs shifted inshore to Mexico and offshore to China,” said Kate Bronfenbrenner, director of labor education research at Cornell University’s School of Industrial and Labor Relations.a>
National Labor Relations Board Overreach Against Boeing Imperils Jobs and Investment Hans A. von Spakovsky James Sherk Legal Memorandum, No. 66 The Heritage Foundation May 11, 2011 "Because they invest less, unionized companies often become less competitive. As a result, these companies create fewer jobs. Research shows that unionized firms shed jobs more frequently and expand less frequently than non-union firms do. ... This is not a coincidence: Unions directly cause these job losses. Employment falls between 5 percent and 10 percent when unions organize a company. ... Going forward, jobs in unionized firms shrink (or grow more slowly) by three to four percentage points a year than they do in non-union firms. ... In the long term, unionized jobs disappear. Such economic decline is the exact effect that unionization has had on the manufacturing sector. ... Non-union manufacturing businesses employed as many workers in 2010 as they did in 1975. However, unionized manufacturing employment fell by 79 percent during the same period. In the aggregate, only unionized manufacturing jobs have disappeared from the economy."
But, your continuously-absurd questioning about the % of unionized manufacturing jobs, completely misses the point. Unions don't just do damage to companies that are currently unionized; they commit terrorism against companies and employees that are non-union; even in RTW states. Who wants to deal with that, if you have other options?
Additionally, labor unions are not the only problem. Federal Government Regulations (especially, but not exclusively) the EPA have caused many companies to offshore, and many new companies to start up overseas.
The Lawsuit Industrytm is another driver of offshoring.
And certainly, Affirmative Action (which also dove-tails with Labor Unions and Trial Lawyers) is another nail in the US Job Coffin.