U.S. stocks fell on Thursday after a key vote in the House regarding a Republican-led health care bill was delayed.

The Dow Jones industrial average fell about 5 points, with UnitedHealth contributing the most losses. The 30-stock index had traded about 96 points higher earlier in the session. The S&P 500 slipped 0.1 percent, having traded 0.45 percent higher earlier, as health care and energy led decliners.

The Nasdaq composite fell around 0.1 percent after rising 0.36 percent at session highs.

"This is almost like a Fed meeting; nobody wants to do anything," said Tom Martin, senior portfolio manager at Globalt.

Dow intraday chart

Source: FactSet

The House vote is crucial for the Trump agenda. Trump has said the repeal and replacement of Obamacare must happen before action can be taken on his other plans, including a major tax reduction. Expectations for such policies had been a boon for the stock market's postelection rally.

Republicans need 215 votes for passage. However, the American Health Care Act's passage in the House has been anything but certain.

"The health care bill is really the first 'put up or shut up' moment of Trump's presidency," said Brad McMillan, chief investment officer at Commonwealth Financial Network. "With the health care bill, we now will find out whether meaningful change can really happen — or not."

A top GOP source told NBC News the House will not vote on the bill on Thursday. Also, House Speaker Paul Ryan's weekly news conference was postponed until further notice.