A new survey from the National Association of Business Economists found business investment growth slowing across the economy, with 84 percent of respondents saying that Mr. Trump’s tax cuts are not encouraging their companies to increase investment. Slowing global growth, particularly in China, has caused other forecasters to lower their growth estimates for the United States this year.

Mr. Trump’s advisers have not yet released their official forecast for the year. But White House officials say they continue to believe the economy will significantly outperform the expectations of more pessimistic projections, for several reasons.

The Council of Economic Advisers’ forecasting model is more bullish than the C.B.O., in part because the administration finds that much of the sluggish growth in the decade preceding Mr. Trump’s election was a hangover from the 2008 financial crisis. The Trump administration also projects a more sustained boost to growth from the $1.5 trillion tax cut package that went into effect last year and deregulatory efforts at agencies across the administration.

Administration officials, who are set to meet with their Chinese counterparts on Wednesday to try to end a trade war, dismiss concerns that trade policy or the shutdown have provided an economic drag.

“We think there's still a very good case for 3 percent this year,” Steven Mnuchin, the Treasury secretary, said Tuesday on Fox Business Network.

Larry Kudlow, the chairman of the National Economic Council, told reporters on Monday that he believed the administration’s economic model was working. “The program of lower tax rates and regulatory rollback and opening up energy and so forth is working and continuing to work,” Mr. Kudlow said in a briefing at the White House. “And I think frankly the optimists, the guys that took the over, will be right.”

Mr. Trump could need that prediction to come true if he hopes to win in 2020. His approval ratings have sagged below 40 percent under the weight of the shutdown, even after recording in 2018 what appears to have been highest annual growth rate since the financial crisis, according to a polling average by the website FiveThirtyEight.