US President Donald Trump delivers remarks on supporting America's farmers and ranchers, flanked by US Agriculture Secretary Sonny Perdue (2nd L), at the White House in Washington, DC, on May 23, 2019.

President Donald Trump on Tuesday promised farmers that China's increasing aggression against U.S. agriculture in the spiraling trade war "will not be able to hurt them" – and vowed that "if necessary" he will give them more aid in 2020.

The Trump administration has already given out billions of dollars in bailouts to farmers threatened by America's tit-for-tat tariffs with China. In May, the Agriculture Department unveiled a $16 billion aid package.

Keeping farmers on his side is a crucial political goal for Trump, who is up for reelection next year and has shown no indication that he is willing to back off his fight with China. The Washington Post reported on Aug.1 that 9 out of 10 counties that supported Trump in the 2016 election have received subsidies related to the trade war.

The stakes for farmers shot up Monday, when Beijing confirmed that it would stop buying U.S. agricultural products altogether. The punishing blow to farmers came as retaliation for Trump's threat last week that the U.S. would slap 10% tariffs on the remaining $300 billion of Chinese goods that don't already have levies.

Trump assured in a tweet, however, that no harm would come to U.S. farmers.

"As they have learned in the last two years, our great American Farmers know that China will not be able to hurt them," Trump wrote Tuesday morning, "in that their President has stood with them and done what no other president would do."

"And I'll do it again if necessary!" Trump added.

Trump TWEET As they have learned in the last two years, our great American Farmers know that China will not be able to hurt them in that their President has stood with them and done what no other president would do - And I'll do it again next year if necessary!

Trump's top economic advisor, Larry Kudlow, backed up Trump's promise later Tuesday morning, telling reporters at the White House that the Trump administration will give farmers more assistance if need be.

China's move to cut off U.S. agriculture from one of its biggest export markets shocked markets that were already leery about the sweeping new tariffs expected from Trump.

The Dow on Monday suffered its worst day of 2019, and all three major stock indexes fell by their biggest percentage margins of the year. Tuesday morning, the Dow clawed back some gains, rising more than 200 points in early trading before paring some of that advance.