Story highlights Deputy Attorney General to brief Senate Thursday afternoon

Democrats had planned to press about a special prosecutor

(CNN) Sen. Lindsey Graham said Thursday he believes the Justice Department's Russia probe is "now considered a criminal investigation," comments he made following the all-senators' briefing with deputy Attorney General Rod Rosenstein.

The South Carolina Republican said he wasn't able to ask specifically if it was now a criminal probe "but the takeaway have is everything he said was that you need to treat this investigation as if it may a criminal investigation".

Rosenstein briefed the US Senate just one day after he turned the political world on its head by appointing a special counsel to investigate possible collusion between the campaign of President Donald Trump and Russian officials meddling in last year's election.

Graham said he thinks "Congress' ability to conduct investigations of all things Russia has been severely limited, probably in an appropriate fashion."

That would make it harder to subpoena records of people who could be subjects of the investigation, he added.

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