President Donald Trump ripped into China in a series of tweets Tuesday just as the two sides are set to resume stalled negotiations toward a much-anticipated trade agreement.

The president claimed that China is not buying more U.S. agricultural products as it promised to do and may be slow-walking the talks as it awaits the outcome of the 2020 presidential election.

"China is doing very badly, worst year in 27 - was supposed to start buying our agricultural product now - no signs that they are doing so. That is the problem with China, they just don't come through," Trump wrote.

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The criticism comes as an entourage led by Treasury Secretary Steven Mnuchin and Trade Representative Robert Lighthizer are in Shanghai to meet with their Chinese counterparts. While U.S. officials have tamped down expectations for a major deal this week, there is hope that at least some progress can be made in the tit-for-tat tariff battle that began more than a year ago.

The stock market struggled at the open in the wake of Trump's trade comments, with the Dow industrials off by about 100 points in early trading.