The problem isn't a lack of candidates, it's a lack of qualified candidates. And the qualified candidates we do get are usually Indian, Chinese, Korean, or from another Asian country, and those candidates often have language barrier problems that make them unfit for the jobs for which they apply.
Unfortunately, education in the U.S. often doesn't prepare workers for the types of STEM jobs that are out there. We have Bachelor or Masters degree holders that are completely inept at performing the most basic engineering skills. We have workers with multiple Doctorates who have no business sense at all, and want to spend most of their time in a lab "tinkering". These people may be "highly trained", but they're trained in the wrong areas (usually full of theory and lacking in any practical application of the theory).
The company I work for made a conscious decision to remove the education requirements, and a flood of GOOD candidates came in. Workers with lots of real-world experience and little formal education. We've experienced a renaissance and are profitable again largely because the quality of our product has increased sharply.
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