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 and his team are looking to determine how much President Trump Donald John TrumpUS reimposes UN sanctions on Iran amid increasing tensions Jeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Trump supporters chant 'Fill that seat' at North Carolina rally MORE knew about his campaign members' contacts with Russian officials and representatives — if anything — during the 2016 race.

Investigators on Mueller's team have questioned Sam Clovis, the co-chairman of Trump's campaign, to determine what Trump knew during the campaign and subsequent presidential transition, Reuters reported Saturday.

“The ultimate question Mueller is after is whether candidate Trump and then President-elect Trump knew of the discussions going on with Russia, and who approved or even directed them,” one source told Reuters. “That is still just a question.”

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Clovis, who currently serves as the senior White House adviser to the Agriculture Department, has already testified before the grand jury for Mueller's probe, and is said to be "cooperative" in the Senate Intelligence Committee's investigation into Russian interference in the 2016 election.

Clovis has garnered attention in the probes after it was revealed that a former foreign policy adviser to the campaign, George PapadopoulosGeorge Demetrios PapadopoulosTale of two FBI cases: Clinton got warned, Trump got investigated Trump says he would consider pardons for those implicated in Mueller investigation New FBI document confirms the Trump campaign was investigated without justification MORE, told him last year about his connections with Russian representatives that could arrange a meeting between then-candidate Trump and Russian President Vladimir Putin.

At the time, Clovis told Papadopoulos that he would "work it through the campaign," but praised his "great work."

Papadopoulos has pleaded guilty to lying to FBI agents about his contacts with Russians while he was working for Trump's campaign.

Mueller is conducting a criminal investigation into Russia's interference in the 2016 election. In particular, he's looking into whether members of Trump's campaign coordinated with Russian government representatives or operatives.

Trump has repeatedly denied collusion between his campaign and Moscow, and has called Mueller's investigation a "witch hunt."

It was revealed in court documents made public last week that Papadopoulos told campaign officials during a March 2016 meeting attended by Trump that he had connections with Russians that could help arrange a meeting between the Republican presidential candidate and Putin.