Stocks shook off morning losses on Monday and surged in the afternoon to send the Standard & Poor’s 500 index to its best day in a week. It’s the latest turn for a market suddenly prone to quick shifts not only day to day but also hour to hour, as investors question whether President Donald Trump will really risk a trade war.

On Monday:

The Standard & Poor’s 500 index rose 29.69 points, or 1.1 percent, to 2,720.94.

The Dow Jones industrial average jumped 336.70, or 1.4 percent, to 24,874.76.

The Nasdaq composite gained 72.84, or 1 percent, to 7,330.70.

The Russell 2000 index of smaller-company stocks added 12.88, or 0.8 percent, to 1,546.05.

For the year:

The S&P 500 is up 47.33 points, or 1.8 percent.

The Dow is up 155.54 points, or 0.6 percent.

The Nasdaq is up 427.31 points, or 6.2 percent.

The Russell 2000 is up 10.54 points, or 0.7 percent.