Sen. Susan Collins, R-Maine, said Sunday it is imperative for congressional committees to recall Democrats involved in Hillary Clinton's 2016 presidential campaign to testify about new findings related to the Trump dossier.

"They absolutely need to be recalled. It's difficult to imagine that a campaign chairman, that the head of the DNC would not know of an expenditure of this magnitude and significance. But perhaps there's something more going on here. But certainly it's worth additional questioning of both two witnesses," Collins told CBS "Face the Nation" host John Dickerson. "And the lawyer. Absolutely. He more than anyone."

Clinton's former campaign chairman John Podesta previously testified before the Senate Intelligence Committee he was unaware who paid for the dossier.

New reports indicate the Washington Free Beacon started funding the project, but it was later financed by the Democratic National Committee and Clinton's campaign.

Special counsel Robert Mueller has also opened a federal investigation into the Democratic-leaning Podesta Group lobbying firm, and Tony Podesta, the brother of Clinton's former campaign manager.

The decision to focus on Podesta was born out of the probe into whether President Trump's campaign associate colluded with Russia, which is also looking into former Trump campaign chairman Paul Manafort's finances.