(CNN) The special counsel's office deliberated at length with Justice Department officials about issuing a subpoena for President Donald Trump to be interviewed, but ultimately the decision was made not to move forward with such a significant investigative step, according to a source familiar with the matter.

For months, Robert Mueller's team had requested a sit-down interview with Trump, but the President's lawyers refused to commit and negotiations continued. Eventually, the special counsel submitted written questions to the President last fall concerning the time frame before the 2016 election, which Trump answered in late November 2018.

The source said the sensitive discussions between Justice Department officials and the special counsel team, and the determination that a subpoena would not be pursued, were based on the perception of the evidence and merits of the issues -- separate and apart from the fact that current department policy dictates that a sitting president cannot be indicted.

While not directly addressing the issue of a presidential interview, Attorney General William Barr's letter to Congress on Sunday offers a further glimpse into how officials at the department didn't believe they had a prosecutable case against Trump on collusion or on the question of obstruction of justice.

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