It is obvious now that Trump will not do better among African Americans than previous Republicans, and may in fact do worse.
From a Republican perspective though, it was worth a shot. Their percentage of the Black vote was already a statistically insignificant part of the overall electorate, so they had nothing to lose by trying something new.
But the idea that all it would take for the Republicans to win more black votes is adopt an anti-free trade stance was kind of hilarious.
Protectionism certainly doesn't hurt with Black voters however.
It only "doesn't hurt" because Republicans get an insignificant percentage of the black vote already.
Basically nothing the Republicans could do would hurt them with the black vote since they can't really get that much lower.