The problem has been building since the 1980s, according to researchers.
Speaking to "Fox & Friends" on Wednesday, the president's eldest son also bragged that he and his brother Eric Trump were "the only sons of billionaires" who could drive a Caterpillar D10.
Republican candidates across the Rust Belt states are facing increased pressure as Trump's falling job approval ratings threaten their own midterm campaigns.
A General Motors union leader says Trump is losing support among manufacturing workers, but experts suggest he knows just how to keep a certain type of voter on side.
Clinton was going to be savaged no matter what, including by liberals and her own party.
The author has joined the investment firm Revolution's Rise of the Rest initiative to fund entrepreneurs in neglected areas.