TPP was a strengthening of the US pacific alliances.
Trump's plan seems to be calling China's bluff. China has one carrier group, the Laoning and it's a repurposed Ukrainian vessel surrounded by inexperienced naval officers. In short, it would have no chance in any confrontation with the US Navy, the most powerful US military branch
China's South China Sea gambit is based on testing boundaries. Trump will likely call the bluff and the Chinese will back off. His initial actions on a one-China policy were buffoonish, but they showed China that their is a wild card in the White House and he has no problem initiating naval combat. It wouldn't take much. US fighter jets - F-22's or F/A-18 overflying Chinese installations would show China what their chances would be pretty swiftly
In a less bellicose situation, the US navy could institute a blockade fairly easily. This hinges on the support of our Pacific allies, so the Filipines are the ally to watch, as they are the only one's who could potentially break and open Chinese sea lanes
On trade, he's calling their bluff. In a trade war, short-term US consumer goods in the US become more expensive and we have to struggle for rare earth metals - fortifying our own companies.
Medium to long-term China loses a massive amount of money as their export sector dries up and social unrest divides their nation. China can't afford social unrest, while the US could theoretically slowly move cheap production to other locations. Mind you, I don't think it's a good idea, but it could happen
Trump's buffoonery is what makes enemies wary. He will do whatever insane thing he says he will and that's dangerous when our adversaries have become lulled into a sense of security and rely on our Middle East obsession