Stocks gave back gains on Tuesday as optimism over an trade pact between the U.S. and China dampened. Plus Apple and Amazon resume their race to be the most valuable company in the world, and Toll Brothers shares plunge after reporting a drop in orders. And two cannabis company stocks head in two very different directions, as Marlboro-maker Altria expresses interest in Cronos, and a short-seller questions Aphria's dealings in Latin America.