Donald Trump was speaking to a mostly white audience when he mentioned "stop-and-frisk." The people in that audience largely support it. If he were speaking to a mostly black audience, he wouldn't mention "stop-and-frisk;" he would try to pander to them. Trump constantly lies and contradicts himself, so it's hard to know what he truly believes.
Yes, I believe that Donald Trump has given up hope of gaining the back community's support especially with the assertion that he would use "stop-and-frisk" to end violence in black communities. "Stop-and-frisk" policy is a dangerous and inherently racist approach to policing. The American Civil Liberties Union admonishes the policy and cites the use of the policy in NYC as a failure.
Yes, I do believe that Trump has given up gaining the support of black communities. However, this was probably always Donald trump's opinion of how to end violence in the black community. Even if I do not agree with his opinions, I am glad he is telling the truth so that people can hear his actual opinions.
Trump hasn't given up on trying to gain the suppose of black communities. On the contrast, I believe that Trump actually thinks that stop and frisk is a good idea. He thought that it "worked" in New York, which shows how out of touch he is with reality. He thinks stop and frisk will only negatively impact criminals. He is still trying, in his own ineffective, unqualified way, to gain their support; he's just failing.