lets start with your premise. "a reduction in taxes would not generate sufficient gains(economic growth) to cover the amount of lost". Why do you assume the default position is always one in which current spending levels must be retained? Where is that written? I'm not defending Trump. That's not my job and it's not something I care to do. This point exists outside of Trump. ALL liberals believe that whatever the government spends today is the minimum that the government must spend tomorrow. There is never a retraction, so no, I reject your claim that he lacks the knowledge. As to the Laffer curve, you clearly don't understand it. It doesn't come anywhere close to approximating the point Laffer was trying to make. Also you do not know it would leave a deficit, because firstly, taxes are not linear, and secondly you cannot account for all the other issues that would affect whether there is a deficit, or how large it is. And your phrasing is HILARIOUS. "It would only leave a deficit" like we haven't had one of those every year since Coolidge, and like Obama hasn't added more to the national debt in his 2 terms then every president before him combined. But nice try.
Trump is very wrong about free trade though and his protectionism, but liberals are just as guilty as pandering to that contingent. And lets be clear...
Trump is NOT a republican. He is a old school democrat.