Malbim #2: The nation never complained about David's deeds. Even if he ordered to kill him, they would not complain
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. If so, he did not need strategies to appease them. Therefore, [surely he was sincere, and] all know that he did not command to kill him.
David was always careful about his deeds. Had he ordered to kill him, after pretending to want to join with him, people would have complained, especially Bnei Binyan! Some say (refer to 16:7:1:2) that later, Shim'i ben Gera accused David of ordering to kill Avner! (PF)
