Analysts also cited profit-taking as a driver after US stocks rallied strongly on Tuesday.

But sentiment was less upbeat again Wednesday following Trump's free-wheeling speech in Arizona on Tuesday night, in which he lambasted the media and vowed to build the wall "if we have to close down our government."

"The fear of new dysfunction might be having some bearing on what the market is doing today," said Bill Lynch, director of investment at Hinsdale Associates.

Analysts are also looking ahead to Friday's summit of central bankers, which comes amid unease over a shift from the easy-money policies of recent years.

The Dow Jones Industrial Average fell 0.4 percent to 21,812.09.

The broad-based S&P 500 dropped 0.4 percent to 2,444.04, while the tech-rich Nasdaq Composite Index lost 0.3 percent at 6,278.41.

Wal-Mart Stores shed 0.1 percent and Google parent Alphabet rose 0.3 percent after the two companies announced they were teaming up in an attempt to challenge Amazon's growing dominance in online shopping through voice-activated ordering of goods on Google Express.