Special counsel Robert Mueller Robert (Bob) MuellerCNN's Toobin warns McCabe is in 'perilous condition' with emboldened Trump CNN anchor rips Trump over Stone while evoking Clinton-Lynch tarmac meeting The Hill's 12:30 Report: New Hampshire fallout MORE is investigating events that took place during the Republican National Convention in 2016, Reuters reported Thursday.

Mueller is looking at an event attended by both then-Sen. Jeff Sessions Jefferson (Jeff) Beauregard SessionsGOP set to release controversial Biden report Trump's policies on refugees are as simple as ABCs Ocasio-Cortez, Velázquez call for convention to decide Puerto Rico status MORE (R-Ala.) and former Russian Ambassador Sergey Kislyak.

He is also looking into how language critical of Russia was removed from a section of the GOP platform on Ukraine.

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Sessions, now the attorney general, recused himself from the Justice Department's probe into Russian election interference after it was revealed that he had contact with Russian officials during the Trump campaign and failed to reveal that contact during his Senate testimony. Sessions acted as an adviser and surrogate for the campaign.

The attorney general said that he did not recall the contacts with Russian officials at the time of his original testimony, but remembered them after reading media reports.

Mueller's team has interviewed Sessions.