The new year began with another round of choppy trading on Wall Street, as stocks opened sharply lower but recouped their losses after a rise in oil prices lifted shares of energy producers.

Volatility has been a defining characteristic of the stock market lately. Investors are trying to gauge the odds of an economic slowdown in the United States, and how such an event might be affected by rising interest rates, uncertainty in American politics and a trade war with China.

[Wall Street’s stock pickers are still hopeful about the year ahead, but here are four things they’re worried about.]

The tone on Wednesday was initially set by fresh evidence that the Chinese economy, the world’s second largest, is slowing. Factory activity in the country fell last month, according to government and private data released this week, an indication that the trade war is beginning to weigh on Chinese manufacturing.