China's President Xi Jinping (L) and US President Donald Trump attend a welcome ceremony at the Great Hall of the People in Beijing on November 9, 2017.

Add President Trump to the list of those hurt by his trade war.

A new NBC News/Wall Street Journal poll shows Americans growing more uneasy about Trump's handling of the economy, which has been one of his principal strengths. That erosion comes in tandem with rising public support for free trade as the Trump administration's tariff conflict with China rattles financial markets and business confidence.

By a narrow 49%-46% margin, Americans still approve of Trump's handling of the economy. But that's down from 51%-41% approval in early May and an even more robust 50%-34% in July 2018.

At the same time, Americans now say they approve of free trade by 64%-27%, a margin of better than two to one. That's up from 57%-37% early in Trump's presidency, and 51%-41% near the end of President Obama's tenure.

That more positive assessment was driven most sharply by political independents, who now embrace free trade by a 77%-15% margin; among Democrats, the margin is 73%-20%. But even Trump's fellow Republicans have turned positive toward free trade, 52%-39%, after viewing it more skeptically early in his administration.

Trump's overall approval ticked down slightly in the survey to 43% from 45% in July. That remains within the range of earlier results for a president whose ratings with a sharply-polarized electorate have stayed remarkably stable.

Public sentiment about Trump's re-election campaign remains similarly stable. Just 40% of Americans say they plan to vote for him in 2020, up two points from last December. The proportion planning to vote against him stayed at 52%.

The survey found modestly increased support for a ban on military-style assault weapons in the wake of recent mass shootings. A 62% majority now express support for a ban, up from 51% in June 2016.

Large majorities also back expanded background checks for gun purchasers, "red flag" laws to identify dangerous individuals, and a voluntary program in which the government would buy back firearms from current owners. But the poll also showed the limits of the public's appetite for pressuring Congress to act.

Nearly half of Americans, 45%, said they worried the government will go too far in restricting gun rights, while 50% worry the government may not go far enough. Meantime, the survey showed the proportion of Americans who say someone in their household owns a gun has risen to 46%, up from 42% in previous surveys.

Americans have not been impressed by Trump's response to recent mass shootings in Dayton and El Paso. By 52%-36%, the poll shows they disapprove of how he has handled the aftermath of those tragedies. A 54% majority says that the language the president uses in his speeches and on Twitter bears significant responsibility for the shootings.

The telephone survey of 1,000 adults, conducted Aug. 10-14, carries a margin for error of 3.1 percentage points.