McCain: Mueller must be allowed to finish investigation 'unimpeded'

Sen. John McCainJohn Sidney McCainEx-Montenegro leader fires back at Trump: ‘Strangest president' in history McCain: Trump plays into 'Putin's hands' by attacking Montenegro, questioning NATO obligations Joe Lieberman urges voters to back Crowley over Ocasio-Cortez in general MORE (R-Ariz.) on Sunday praised special counsel Robert MuellerRobert Swan MuellerSasse: US should applaud choice of Mueller to lead Russia probe MORE amid speculation that President TrumpDonald John TrumpIran claims it rejected Trump meeting requests 8 times ESPY host jokes Putin was as happy after Trump summit as Ovechkin winning Stanley Cup Russian ambassador: Trump made ‘verbal agreements’ with Putin MORE may be preparing to fire him. 

“Special Counsel Mueller has served our country with honesty and integrity. It’s critical he be allowed to complete a thorough investigation into Russia’s interference in the 2016 election — unimpeded,” McCain tweeted.

Trump has at various times this weekend lashed out at the FBI, Department of Justice and Mueller probe, prompting speculation he might call for Mueller's firing.

On Saturday, he asserted that Mueller's investigation should never have been opened in the first place. On Sunday, he attacked the makeup of Mueller's team, claiming it is unfairly stacked with Democrats. Mueller himself is a Republican.

The tweets came shortly after Trump's lawyer, John Dowd, called on Deputy Attorney General Rod RosensteinRod Jay RosensteinKey GOP lawmaker throws cold water on Rosenstein impeachment The Hill's Morning Report — Trump’s walk-back fails to stem outrage on Putin meeting Trump's Russia remarks put intel chiefs in tough spot MORE, who oversees Mueller's investigation, to shut down the probe.

On Sunday, lawmakers from both sides of the aisle warned Trump against firing the special counsel. Sen. Lindsey Graham (R-S.C.) suggested such an action would be "the beginning of the end" of Trump's presidency.

Mueller has obtained guilty pleas from three former Trump associates, and indicted former Trump campaign chairman Paul ManafortPaul John ManafortJudge rejects Manafort motion to suppress evidence seized from residence Mueller probing Roger Stone following Russian hacker indictment: report Judge rejects Manafort's bid to move trial further from DC MORE. He also filed charges against 13 Russians and three Russian organizations for allegedly interfering in the 2016 election.