Sen. Lindsey Graham, R-S.C., expressed confidence in special counsel Robert Mueller's investigation into Russia's election interference, even as other congressional Republicans have cast doubt on whether it has remained non-partisan.

In an interview Sunday on CBS' "Face The Nation," Graham said everyone should let the investigation, which is also looking into whether President Trump's campaign colluded with Russia, play out.

"In 2018, this investigation will go forward," Graham said. "It will be an investigation conducted without political influence. The president needs to focus on his day job. I need to focus on being a senator. We all need to let Mr. Mueller do his job. I think he’s the right guy at the right time."

Trump himself has often described the investigation as a "witch hunt" and denied that he was involved in any collusion but he said in a separate recent interview he trusted Mueller to be fair in his probe.

Evidence, including text message communications, surfaced in recent weeks apparently showing some agents involved in the investigation held negative views about Trump during the election, leading Republicans to claim that the probe is tainted by partisanship.