The current U.S. ambassador to China, Terry Branstad, announced he would step down from his position on Monday, amid high tensions between Washington and Beijing. President Donald Trump has reportedly asked Branstad to help him on the campaign trail. 

“I thank Ambassador Terry Branstad for his more than three years of service to the American people as U.S. Ambassador to the People’s Republic of China,” Secretary of State Mike Pompeo tweeted on Monday. 

Branstad, a Republican, previously served as the governor of Iowa. He served in the position from 1983 to 1999 and from 2011 to 2017, making him the longest-serving governor in U.S. history. 

Branstad, 73, became the U.S. envoy to China in July 2017. Branstad had frequently visited China as Iowa’s governor, and began a friendship with current Chinese President Xi Jinping in the 1980’s. 

During his tenure as ambassador, Trump waged a trade war with Beijing, levying tariffs on Chinese goods. In January, the U.S. and China agreed to a “Phase One” trade deal, where Beijing would buy an additional $200 billion in American goods over the next two years, with Trump agreeing to suspend planned tariff increases on Chinese products. 

“I am proudest of our work in getting the Phase One trade deal and delivering tangible results for our communities back home," Branstad said about his resignation. "Our goal remains meaningful, measurable results for American families. We have made significant progress and we will not stop pressing for more.”

Branstad’s departure comes amid strained ties between the U.S and China. Trump has blamed China for the ongoing COVID-19 pandemic and condemned a new Beijing-backed security law in Hong Kong. Trump has also initiated a crackdown on Chinese tech companies, such as telecommunications firm Huawei and Bytedance, the creator of the TikTok video app.