Hunter Biden, left, embraces his father, President-elect Joe Biden, in Wilmington, Del., Nov. 7. Hunter Biden says he has learned from federal prosecutors that his tax affairs are under investigation.

WILMINGTON, Del. — A federal investigation into the finances of President-elect Joe Biden’s son, Hunter, threatens to embolden congressional Republicans, who have shown little willingness to work with the incoming president.

“Joe Biden needs to pledge today that he will cooperate with the federal investigation and answer any questions under oath,” Sen. Josh Hawley, R-Mo., said Thursday, “and that if he is sworn in as president, no federal investigator or attorney working on the Hunter Biden criminal case will be removed.”

Hunter Biden has long been a source of worry for his father’s campaign and was the subject of accusations by President Donald Trump and his allies.

News of the probe, which was revealed Wednesday and scrutinizes some of Hunter Biden’s Chinese business dealings and other transactions, caught most of his father’s staffers by surprise.

The president-elect had no public appearance Thursday as he moved forward with filling out his administration. Most notably, the probe casts a spotlight on one of Biden’s most important choices: his attorney general. Alabama Sen. Doug Jones and federal Appeals Court Judge Merrick Garland have emerged as the leading contenders, three people familiar with the matter told The Associated Press this week. Biden’s choice now will be scrutinized for any perceived loyalty to the president-elect and bias in any probe of his son. Both Garland and especially Jones have longtime ties to Biden.

The president-elect himself is not a subject of the investigation. And Biden aides believe that because other Hunter Biden stories have blown over, this will too.

Federal investigators served a round of subpoenas Tuesday, including to Hunter Biden, according to a person familiar with the investigation who spoke on condition of anonymity.

The federal investigation, centering on potential tax crimes, had been going on at least a year before Biden announced his 2020 candidacy. Investigators did not reach out in the weeks prior to voting because of a department policy surrounding elections that prohibits overt investigative acts.