Senate Homeland Security and Governmental Affairs Committee Chairman Ron Johnson Ronald (Ron) Harold JohnsonThe Hill's Morning Report - Sponsored by The Air Line Pilots Association - White House moves closer to Pelosi on virus relief bill Second GOP senator to quarantine after exposure to coronavirus GOP-led panel to hear from former official who said Burisma was not a factor in US policy MORE (R-Wis.) said Sunday that Democratic presidential front-runner Hillary Clinton Hillary Diane Rodham ClintonJeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Momentum growing among Republicans for Supreme Court vote before Election Day Warning signs flash for Lindsey Graham in South Carolina MORE's use of a private email server while secretary of State could have played a role in Russia's invasion of Crimea and eastern Ukraine.

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"You have to assume that our enemy and adversaries had to have had access to every email that ever went over her private server," Johnson said on CBS's "Face the Nation."

"Did it affect their actions — as it's related to, for example, [Russian President] Vladimir Putin's invasion of Crimea or eastern Ukraine? What about the negotiations with Iran? What about Assad?"

Johnson, who has shied away from formally endorsing presumptive GOP nominee Donald 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, has been a vocal critic of Clinton.

Republican criticism of Clinton has escalated during the past week after a watchdog report showed she didn't comply with the State Department's record-keeping policies and used a personal server without permission while secretary of State.