It is tempting to say that Trump is clueless when he makes nonsensical comments such as this, but I don't believe he is. I think he knows perfectly well that it's a crock - but all he needs is for enough people to believe it.
It's hard to know with Trump. I don't believe he's stupid, & at times (in the past) he has taken some perfectly reasonable positions. However, he has some serious ... character flaws ... that make him temperamentally unsuited to be President of the most powerful country on earth, regardless of any policy positions he may take.
Narcissism:
"1. Has a grandiose sense of self-importance (e.g., exaggerates achievements and talents, expects to be recognized as superior without commensurate achievements).
2. Is preoccupied with fantasies of unlimited success, power, brilliance, beauty, or ideal love.
3. Believes that he or she is “special” and unique and can only be understood by, or should associate with, other special or high-status people (or institutions).
4. Requires excessive admiration.
5. Has a sense of entitlement, i.e., unreasonable expectations of especially favorable treatment or automatic compliance with his or her expectations.
6. Is inter-personally exploitative, i.e., takes advantage of others to achieve his or her own ends.
7. Lacks empathy: is unwilling to recognize or identify with the feelings and needs of others.
Is often envious of others or believes that others are envious of him or her.
8. Shows arrogant, haughty behaviors or attitudes."
In other news: The Congressional black caucus PAC has come out with a strong endorsement of Clinton. This is going to prove a serious obstacle to Sanders gaining momentum with black voters IMO.