While stocks pared losses as the session wore on, all but four of the S&P 500's 11 sectors ended lower, with financials leading the decline a day ahead of the first major earnings reports in that sector. The S&P had risen 6.4 percent since the Nov. 8 election.

Trump on Wednesday dashed investor hopes for new details on his policy plans in his first news conference since the election, instead lashing out at U.S. spy agencies and media companies for what he called a "phony" Russia dossier and repeated promises to reform healthcare policies.

On top of policy uncertainty, the market is missing stock buyback support in the quiet period ahead of earnings and individuals are putting more money into bonds than stocks, according to Jeffrey Kleintop, chief global investment strategist at Charles Schwab in Boston.

"Companies can't buy shares, and individuals all of a sudden stopped buying since the election. That could be the reason we're seeing a little bit of a gap down today," said Kleintop, but the dip could be temporary if earnings beat expectations.

Kleintop cited Investment Company Institute's data on Wednesday showing the biggest cash flows to bond funds from stock funds since the election.

The Dow Jones Industrial Average .DJI fell 63.28 points, or 0.32 percent, to close at 19,891, the S&P 500 .SPX dropped 4.88 points, or 0.21 percent, to 2,270.44 and the Nasdaq Composite .IXIC dipped 16.16 points, or 0.29 percent, to 5,547.49.

The S&P had fallen as much as 0.9 percent earlier in the session, and its financial index .SPSY finished off 0.74 percent, as yields on long-dated bonds fell.

Brad McMillan, Chief Investment Officer for Commonwealth Financial in Waltham, Mass. said the stock market's continued proximity to its post-election peak was a positive sign.

"The fact we're still bouncing along the ceiling means to me that everybody's still pretty optimistic," said McMillan.

"The population is confident. They're willing to spend and they're making more money and able to spend. That's good news," he said.

The S&P's healthcare sector .SPXHC ended up 0.07 percent after tumbling 1 percent in the previous day's session because of Trump's comments.

The index was helped by a 0.9 percent increase for Merck (MRK.N) and a 2.5 percent increase for Eli Lilly (LLY.N) after a U.S. appeals court said it could block Teva Pharmaceutical Industries Ltd (TEVA.TA) from selling a generic equivalent of Eli Lilly's top-selling lung cancer drug.

JPMorgan Chase (JPM.N) was one of the biggest drags on the S&P 500 the day before its earnings report was due, losing nearly 1 percent.

Declining issues outnumbered advancing ones on the NYSE by a 1.55-to-1 ratio; on Nasdaq, a 1.96-to-1 ratio favored decliners.

The S&P 500 posted 10 new 52-week highs and four new lows; the Nasdaq Composite recorded 60 new highs and 21 new lows.

More than 6.7 billion shares changed hands on U.S. exchanges, higher than the 6.5 billion average in the last 20 sessions.

(Additional reporting by Yashaswini Swamynathan in Bengaluru; Editing by Steve Orlofsky and James Dalgleish)