President Donald Trump sought to shift blame for turbulent trade negotiations with China to his political opponents, arguing that Beijing would rather negotiate with a “weak” Democrat.

Trump took a shot at his challengers, singling out former Vice President Joe Biden, who is running for the 2020 Democratic presidential nomination, saying China would prefer to negotiate with them. Biden has been criticized in recent weeks for playing down the economic threat posed by China, arguing the U.S. is in a much stronger position than Trump credits it with.

“The reason for the China pullback & attempted renegotiation of the Trade Deal is the sincere HOPE that they will be able to “negotiate” with Joe Biden or one of the very weak Democrats, and thereby continue to ripoff the United States (($500 Billion a year)) for years to come....” Trump tweeted on Wednesday.

In a subsequent tweet, he wrote: “Guess what, that’s not going to happen.”

Trump’s comments underscore the political pressure he’s under to reach a deal with China, with his own party fractured over the merits of tariffs and Democrats looking to blame the president if the trade war seriously damages the U.S. economy.

“The president is correct in asserting what we have to do with China, how he’s doing it though is empowering them to hurt people,” House Speaker Nancy Pelosi said at an event in Washington on Wednesday, after previously citing China’s treatment of Uighurs, a Muslim ethnic minority, and Tibetans, along with the wider issue of human rights.

Trump’s also facing criticism from business leaders over his decision to ratchet up tariffs on $200 billion of Chinese goods to 25 percent from 10 percent as of Friday, despite high-level trade negotiations continuing this week. The S&P 500 Index traded little changed early Wednesday, after declining more than 2 percent in the two days after Trump announced the tariff escalation.

The U.S. Trade Representative’s office took a formal step toward implementing the tariffs on Wednesday by publishing a Federal Register notice confirming the duties will increase as of 12:01 a.m. on Friday. China has said it plans to retaliate a minute after the U.S. duties take effect.

Trump said in another tweet that “China has just informed us that they (Vice-Premier) are now coming to the U.S. to make a deal. We’ll see, but I am very happy with over $100 Billion a year in Tariffs filling U.S. coffers.”

Beijing’s top trade negotiator, Liu He, is traveling to the U.S. on Thursday and Friday for high-stakes talks. U.S. officials have said Chinese negotiators reneged in the past week on provisions in a draft deal the U.S. considered settled. The developments raise the prospect that talks between the U.S. and China to resolve their trade war could collapse entirely.