WASHINGTON (AP) — The special counsel leading the Russia investigation raised the prospect in March of issuing a grand jury subpoena for President Donald Trump, his former attorney said, confirming that investigators have floated the extraordinary idea of forcing a sitting president to testify under oath.

Attorney John Dowd told The Associated Press on Tuesday that special counsel Robert Mueller's team broached the subject during a meeting with Trump's legal team while they were negotiating the terms of a possible interview with the president.

It was not immediately clear in what context the possibility of a subpoena was raised or how serious Mueller's prosecutors were about the move. Mueller is probing not only Russian election interference and possible coordination with Trump associates but possible obstruction of justice by Trump.

Even if Mueller's team decided to subpoena Trump as part of the investigation, he could still fight it in court or refuse to answer questions by invoking his Fifth Amendment protection from self-incrimination.

Dowd's comments come more than a month after he resigned from the legal team, and they provide a new window into the nature of the Trump lawyers' interactions with the special counsel, whom the president has increasingly tried to undermine through public attacks.

On Tuesday, Trump said it was "disgraceful" that a list of proposed questions drafted in response to Mueller's negotiations with the legal team was "leaked" to the news media.

The about four dozen questions were compiled by Trump's lawyers during negotiations with Mueller's investigators earlier this year over the prospect of a presidential interview.

A person familiar with the matter, who insisted on anonymity to discuss ongoing negotiations, told the AP that the president's lawyers extrapolated the list of expected questions based off conversations with Mueller's team about the topics prosecutors wanted to cover in a potential sit down with Trump. The questions reflected what the defense lawyers anticipated Trump would be asked, rather than verbatim queries that Mueller's team provided, the person said.

The Washington Post first reported that Mueller's team raised the possibility of a subpoena for Trump. The New York Times first published the list of questions.

According to the list, the questions range from Trump's motivations for firing FBI Director James Comey a year ago to contacts Trump's campaign had with Russians. Although Mueller's team has indicated to Trump's lawyers that he's not considered a target, investigators remain interested in whether the president's actions constitute obstruction of justice and want to interview him about several episodes in office. They have not yet made a decision about an interview.

In his tweet, Trump said there were "no questions on Collusion" and, as he as many times before, called Mueller's investigation a "Russian witch hunt." He said collusion with the Russians "never existed."

In a second tweet, Trump said: "It would seem very hard to obstruct justice for a crime that never happened."

The questions do appear to indicate that Mueller is looking into possible collusion. Some touch on Russian meddling and whether the Trump campaign coordinated in any way with the Kremlin. In one question, Mueller asks what Trump knew about campaign staff, including his former campaign chairman Paul Manafort, reaching out to Moscow.

Mueller has brought several charges against Manafort already, including money laundering and bank fraud. None of the charges relates to allegations of Russian election interference and possible coordination with Trump associates, and Manafort has denied having anything to do with such an effort.

The questions also involve key moments from the early months of the Trump administration, including his reaction to Attorney General Jeff Sessions' recusal from the Russia investigation and Trump's firing of his national security adviser, Michael Flynn.

One question asks whether there were any efforts to reach out to Flynn "about seeking immunity or possible pardon" ahead of his guilty plea last year. Flynn is now cooperating with Mueller.

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Associated Press writers Mary Clare Jalonick and Darlene Superville contributed to this report.