The tax issues came to the attention of F.B.I. agents after they opened the money laundering investigation into Hunter Biden’s financial affairs in late 2018, under the attorney general at the time, Jeff Sessions, according to several people familiar with the inquiry.
What prompted the F.B.I. inquiry remains unclear. Former law enforcement officials said that though the money-laundering aspect of the inquiry appears to have died out, investigators with the Internal Revenue Service continued to examine Mr. Biden’s taxes.
By early 2017, Mr. Biden and his first wife, Kathleen, who were then estranged, owed $313,970 in taxes, and had “maxed-out credit-card debt” and “double mortgages on both real properties they own,” according to a filing she submitted in their divorce.
The next year, the I.R.S. issued a lien against the pair, who were by then divorced, for $112,805 in unpaid taxes from 2015. Those taxes appear to have been paid off by March of this year, when the lien was released.
Separately, the city government of Washington, D.C., where Mr. Biden had lived, issued liens against him in July totaling nearly $454,000 for unpaid taxes from 2017 and 2018. Those liens were released less than one week later, according to tax records.
Mr. Biden has long been an intense target of Mr. Trump and his allies over the range of business ventures he pursued around the world during his father’s time as vice president and beyond.
He was paid $50,000 a month or more to serve on the board of Burisma, a Ukrainian energy company owned by an oligarch who was widely seen as corrupt, advised a wealthy Romanian business executive facing corruption charges and invested in a private equity fund linked to the Chinese government.