Ex-Chicago Mayor Rahm Emanuel and former Under Secretary of State for Political Affairs Nicholas Burns are among the leading candidates for U.S. ambassador to China, a person familiar with the matter said.

The Biden administration is looking for someone with deep political ties or diplomatic experience for the crucial posting, according to the person, who asked not to be identified discussing the internal deliberations.

The ambassador to Beijing will act as a critical bridge between the world’s two largest economies after the Biden administration signaled that it plans to maintain former President Donald Trump’s tough stance toward Beijing while also allowing for possible areas of cooperation on issues such as climate change.

Secretary of State Antony Blinken has called China the preeminent nation-state challenge facing the U.S. while Secretary of Defense Lloyd Austin has described China as the top threat to America’s military supremacy.

Spokespersons for the White House and State Department declined to comment.

Earlier discussions for the envoy role included consideration of a number of academics, including David Shambaugh, a George Washington University professor, and several business executives. Former U.S. Trade Representative Charlene Barshefsky was also discussed as a potential nominee, two people familiar with the Biden administration’s deliberations said. She has ruled herself out from consideration after discussions with the White House, one person said.

Chief of Staff

The politically savvy and combative Emanuel, who was White House chief of staff to President Barack Obama, has been considered for various administration roles since President Joe Biden’s November election victory. Emanuel, who NBC previously reported is a possible candidate for the ambassadorship, didn’t immediately respond to a request for comment.

Emanuel was an early contender for transportation secretary, a role that eventually went to former Mayor Pete Buttigieg. Emanuel is also being considered as a possible candidate for U.S. ambassador to Japan, the person said.

Emanuel didn’t respond to repeated phone calls seeking comment.

Emanuel’s nomination would probably face opposition within the Democratic Party. Progressives have raised concerns about his record in the Obama administration, including his opposition to a larger stimulus bill in 2009 and what they see as an unwillingness to work with the left. They and some civil rights groups, including the NAACP, have said that his handling of the police killing of 17-year-old Laquan McDonald in Chicago should disqualify him from joining the Biden administration.

Burns served in the government for 27 years and is currently a professor at the Harvard Kennedy School. He was U.S. ambassador to NATO from 2001 to 2005 and ambassador to Greece from 1997 to 2001. Two people said he was being weighed as potential envoy to Beijing.

Over the years, ambassadors to Beijing have included career diplomats such as Winston Lord as well as political figures such as former Washington state Governor Gary Locke and former Iowa Governor Terry Branstad.