McGahn served as Donald's Trump's campaign lawyer and spearheaded the president's successful push to pack the bench with conservative judges.
President Trump and the White House had stayed mostly silent in the wake of Paul Manafort's conviction and Michael Cohen's guilty plea, but Wednesday he returned to Twitter and taped a TV interview.
The special counsel noted that the legal guidelines suggest a sentence of zero to six months. George Papadopoulos pleaded guilty to lying to the FBI about contacts with Russians.
On Twitter, the president called the probe a "hoax," asked attorney general to end the "rigged witch hunt" and referenced legendary mobster Al Capone.
Trump's former attorney reportedly claims Trump knew in advance of the 2016 meeting between Donald Trump Jr. and other campaign officials and Russians peddling dirt on Hillary Clinton.
The Ohio congressman and Freedom Caucus member announced Thursday that he will challenge the expected bid by Majority Leader Kevin McCarthy, who is current speaker Paul Ryan's hand-picked successor.
National security adviser John Bolton referred to the special counsel investigation in announcing that Russia's president won't visit the United States this year.
The leaders held a stunning joint news conference after speaking privately for about two hours, just days after a grand jury indicted 12 Russian intelligence agents on election-related charges.
President Trump's lawyer said he and the rest of the president's team are "very comfortable" with Cohen working with investigators, as long as he tells the truth.
Trump held a wide-ranging news conference on the White House lawn Friday morning, saying the threat of nuclear war with North Korea is "largely solved."