DECORAH, Iowa — Seated in a motor coach emblazoned with his name late last week, Joe Biden took a breath and prepared himself to answer yet another question on a subject he clearly doesn’t like to discuss: his son Hunter’s business dealings in Ukraine.

“My son spoke, speaks for himself. He’s a 47-year-old man. He didn’t do a single thing that was illegal or wrong,” Biden said, adding a short while later: “I’m going to talk about Trump. Trump is the one who violated the Constitution.”

In the months since President Trump began attacking the Bidens over Hunter’s lucrative job on the board of the Ukrainian gas company Burisma during his father’s time as vice president, the elder Biden has been reluctant to talk about a matter that is both personally painful and politically awkward.

When he has, he has struggled to provide a coherent explanation — insisting his son did nothing wrong while also promising that no one in his family would serve on foreign boards if he was elected.

But in recent days, as Biden has sought to pump new life into his campaign with a bus tour across Iowa and multiple media interviews, he has also submitted himself to a conveyor belt of questions about his son. He has addressed the matter on at least five occasions in the past week — at times offering responses that seemed to put more distance between himself and his son’s decision to join the Burisma board.

He told NPR that even though he was distraught at the time about his oldest son, Beau, battling brain cancer, his staff should have informed him of Hunter’s business dealings. “I never, never heard that once at all,” he said, adding, “They should have told me.” (The New Yorker reported in July that Amos Hochstein, the Obama administration’s special envoy for energy policy, did raise the issue with Biden.)

Biden told Axios that he trusted his son to do the right thing, saying there was “nothing on its face that is wrong” about his son doing business in another country. But he also said that he didn’t know what exactly his son did while on the board.

The most memorable moment of the “No Malarkey!” bus tour of Iowa came when Biden called a voter a “damn liar” for saying he had sent his son “over there to get a job and work for a gas company that he had no experience with gas or nothing, to get access to the president.”

The voter’s facts were off. Hunter Biden was appointed to the board, and there is no evidence that Joe Biden played any role in getting him the job or provided access to the Obama administration. Moreover, there is nothing to back up Trump’s claim that Biden pressured the Ukrainian government to get rid of a prosecutor investigating Burisma to protect his son.

Nonetheless, the viral moment highlighted the extent to which Hunter Biden’s overseas work has remained a persistent question for his father’s presidential campaign.

Even as House Democrats are preparing for a vote to impeach Trump for pressuring Ukraine to announce an investigation of the Bidens, the impeachment proceedings have also raised the issue of whether the younger Biden’s overseas work created a potential conflict of interest for his father. One career State Department official, George Kent, told investigators that he had raised concerns about Hunter Biden’s appointment to the Burisma board but that he was turned away by a Biden staffer after being told Biden didn’t have the “bandwidth” to deal with the issue as his other son, Beau, was battling cancer.

An October AP-NORC poll found a 69 percent majority of Americans said it was “inappropriate” for Hunter Biden to serve on the board of a Ukrainian energy company while his father was vice president.

The issue remains an emotionally difficult one for Biden, and he did not do any special preparations regarding what to say in the lead-up to his recent spate of appearances, according to people close to him who spoke on the condition of anonymity because they were not authorized to discuss campaign strategy.

One person said Biden has realized the questions aren’t going to stop and has had more time to think about how to best answer them.

“He’s very savvy, very intelligent,” the person said. “He sees . . . how the story is playing.”

Biden’s campaign would not say whether it is changing how Biden addresses questions about his son and Ukraine. A spokesman pointed to the baseless claims by Trump and his allies that Biden as vice president pushed for the Ukrainian prosecutor’s firing to protect his son. In fact, Biden had been advocating bipartisan U.S. policy.

“The facts of the matter haven’t changed, and neither will our aggressive response. Donald Trump’s claims about Joe Biden and his family have been thoroughly disproven by every independent news organization that’s looked into them,” Biden spokesman T.J. Ducklo said in a statement.

The issue is likely to intensify in January, when Republicans who run the Senate are expected to focus on the Bidens during Trump’s impeachment trial, which would probably take place in the weeks before the Iowa caucuses.

Biden signaled in his recent comments that he intends to try to turn the Ukraine issue back onto Trump — as he did Thursday when Telemundo anchor José Díaz-Balart asked whether it was wrong for his son to take the Burisma post.

“I’m not gonna — and I know you’re not intending to do this — play the game to take the eye off the culprit,” he told Díaz-Balart. The president, he said, “has held up $400 million in aid that — for a Ukrainian military when Ukrainians are dying, getting shot dead by Russians in uniforms without marks on them. . . . That is criminal.”

When asked by Axios about the impact of his son’s business dealings on his chances to become president, Biden shot back, “Look, the American public knows me,” and he point to issues with the Trump family’s business dealings.

Biden has made clear that he sees the Ukraine matter as a chance to frame a potential general election matchup as a contrast between his integrity and Trump’s.

“Hey, look, here’s the deal,” he told reporters on his bus Friday night. “This is all about what Trump wants to talk about, anything to divert the subject from his violation of the Constitution.”

“Every time I’ve been asked about it, my response has been, this is about Donald Trump. Period. Period. Period. [He’s] the only one who’s done anything wrong.”