Trump was weak attacking Cruz, but he was excellent on the issues (China, Muslim ban, etc).
He demonstrated knowledge on one issue: trade with China. The rest was hand-waving and slogans.
His conclusion was so shockingly vacuous ("we won't do stupid things. We'll make America great again") that Maria was caught smirking.
Cruz was in command with respect to every issue, and won the birther showdown with Trump.
Trump foolishly brought the public's attention to Cruz before the debate with his silly birther attacks. With the additional attention, Cruz had his best performance so far.
The Luntz focus group agreed that Cruz won the debate.