Even some of his own aides and allies were alarmed by his behavior, seeing it as the flailing of a president increasingly anxious over the dark clouds some have detected hovering over an economy that until now has been the strongest selling point for his administration. They privately expressed concern that he was hurting the economy and was doing lasting damage to his own prospects for re-election…

“Uncertainty is generally bad for the economy, as firms put off making fixed investments until the uncertainty is resolved,” said N. Gregory Mankiw, a Harvard professor and former chief White House economist for President George W. Bush. “Of course, uncertainty is an inevitable fact of life. But uncertainty caused by erratic policymakers is gratuitous.”…

Mr. Trump’s tweets caught most of his advisers and staff by surprise. His advisers have grown concerned that he is creeping perilously close to turning what they had hoped would be his signature issue into a liability. His moves risk scaring away voters, including some of his own backers.

His aides believe Mr. Trump is being urged on by Robert Lighthizer and Peter Navarro, his trade advisers, who generally share the president’s hostile view of China and who advocated a confrontational path with tariffs. Some said they have filled a void left by Mick Mulvaney, the acting chief of staff, who has not weighed in forcefully.