The trade war is back on — at least as far as investors are concerned.

Stocks sank on Tuesday, as President Trump threatened China with further tariffs, just days after the two countries agreed to a cease-fire in their escalating economic conflict. Referring to himself as a “Tariff Man,” Mr. Trump, in a series of tweets, deepened the murkiness surrounding the trade agreement, while members of his economic team talked down the prospects of a broad deal.

The fear is that a lasting trade war will undermine the global growth at a time when some of the world’s largest economies are already slowing down, and the United States, a standout performer, is also expected to slow.

The global and domestic worries are undercutting the prospects for manufacturers, technology companies, regional banks and airlines, intensifying the sell-off in stocks. The S&P 500 lost more than 3 percent on Tuesday, after rallying the day before on the hope of a deal with China.

“They actually want to see a positive resolution where this problem is solved so they don’t have to worry about it,” said Randy Watts, chief investment strategist at the brokerage firm William O’Neil & Company.