The Dow Jones Industrial Average ended down 0.3 percent at 23,062.40.

The broad-based S&P 500 declined 0.1 percent to 2,485.74, while the tech-rich Nasdaq Composite Index edged up 0.1 percent to 6,584.52.

Markets bounced repeatedly between positive and negative territory on a quiet news day characteristic of the normally sleepy period between Christmas and New Year.

Stocks plunged on Monday amid worries that President Donald Trump could fire Federal Reserve Chief Jay Powell and unease after Treasury Secretary Steven Mnuchin spoke with banks in an effort to reassure the markets that instead amplified doubt.

But stocks surged on Wednesday in a relief rally spurred in part by White House assurances that Powell's job was secure.

Major US indices are almost certain to end the year with losses. While investors aren't sure what 2019 will bring, more big swings are certainly possible.

"We're still working through the volatility," said Manulife senior portfolio manager Nate Thooft.

"I don't think we'll see meaningfully lower lows, but a retest is certainly not out of the question."