WASHINGTON >> A federal grand jury has heard testimony in recent months about Hunter Biden’s income and payments he received while serving on the board of a Ukraine energy company, according to two people familiar with the probe.

It remains unclear whether he might be charged. But the grand jury activity underscores that a federal tax investigation into President Joe Biden’s son that began in 2018 remains active as prosecutors continue to examine foreign payments and other aspects of his finances.

A lawyer for Hunter Biden did not return a phone message and email seeking comment today. A Justice Department spokesman referred a request for comment to the U.S. attorney’s office in Delaware, which is handling the investigation. A spokesperson for the office did not return a phone message seeking comment.

The people familiar with the investigation could not discuss details of the ongoing probe publicly and spoke to AP on condition of anonymity.

No matter how the investigation resolves, it has already presented a political headache for the Biden administration and could lead to an even bigger one, particularly if Republicans who have seized on the probe to attack the president retake control of the House in midterm elections later this year. Republicans would then control congressional committees and shape the focus of any investigations.

A White House that has sought to deflect questions about law enforcement matters to the Justice Department was asked this week whether it stood by the president’s assertion in a 2020 debate that his son had not had unethical business dealings with Ukraine or China. White House communications director Kate Bedingfield said yes.

The investigation could also force a delicate decision for the Justice Department, which has sought to assert its independence and has publicly stressed its willingness to let the facts and evidence, not political decisions, guide its investigative and charging decisions.

Attorney General Merrick Garland has not shed any light publicly on the investigation. But the Justice Department did leave in place the top federal prosecutor in Delaware — David Weiss, a Trump administration holdover — presumably as a way to ensure continuity.

Hunter Biden confirmed the existence of an investigation into his taxes in December 2020, one month after the presidential election. He said in a statement at the time that he was “confident that a professional and objective review of these matters will demonstrate that I handled my affairs legally and appropriately, including with the benefit of professional tax advisors.”

The Associated Press reported later that month that a subpoena served on the younger Biden sought information related to more than two dozen entities. One was Burisma, a Ukrainian gas company whose board he had joined when his father was vice president. That move sparked concerns about a potential conflict of interest given that elder Biden was deeply involved in U.S. policy toward Ukraine during the Obama administration.

The breadth of the subpoena highlighted the wide-ranging scope of the investigation into Hunter Biden, though there is no indication that the probe includes any scrutiny of the president himself. Biden has said he did not discuss his son’s international business dealings with him and has denied having ever taken money from a foreign country.

Witnesses in recent months have been questioned about payments Hunter Biden received while serving on the Burisma board, the people familiar with the probe said.

Republicans tried making Hunter Biden’s business dealings in Ukraine a prominent issue during the 2020 presidential election.

A year earlier, then-President Donald Trump tried pressuring his Ukrainian counterpart, Volodymyr Zelenskyy, to launch investigations into the Bidens at the same time Zelenskyy was seeking military aid from the U.S.

Trump was later impeached by the House over the phone call but was acquitted by the Senate.