Trump's personal attorneys said in a January letter to special counsel Robert Mueller obtained by The New York Times last week that Trump "dictated a short but accurate response to The New York Times article on behalf of his son, Donald Trump, Jr".
Mr Giuliani underscored one of the main arguments in a newly unveiled letter sent by Mr Trump's lawyers to Mr Mueller back in January: A president can not be given a grand jury subpoena as part of the investigation into foreign meddling in the 2016 election. Giuliani told ABC's "This Week".
But a three-page memo from the Justice Department's Office of Legal Counsel that was written in 1974 - days before President Richard Nixon resigned - says the President can not pardon himself because "no one may be a judge in his own case".
Trump got the Twitter ball rolling early on Monday with some tweets touting the success of his first 500 days in office.
"This is the president's decision ultimately, " he said.
Sanders again professed the president's innocence when she was asked about another Trump tweet that declared Mueller's investigation "totally UNCONSTITUTIONAL!"
As for talk of Trump pardoning himself, Biggs said it's premature, since there is no evidence a crime was committed, let alone charges filed against him.
Trump's assertion that Mueller's investigation is illegal came only after 13 months of the investigation.
Sanders said the same when asked whether Trump has consulted with the Office of Legal Counsel on his pardoning power.
"If he shot James Comey, he'd be impeached the next day", Giuliani said.
"He has no intention of pardoning himself, " Giuliani added.
Harvard law professor Jack Goldsmith told the Times the law is unclear regarding "the intersection between the obstruction statutes and the president exercising his constitutional power to supervise an investigation in the Justice Department". "Despite that, we play the game because I, unlike the Democrats, have done nothing wrong!" - he initially wrote. "You can read it that (pardon power) pretty much applies to anybody, but I don't think that makes much sense".
Giuliani also said during an interview Sunday on NBC News' "Meet the Press" that "the straight, unvarnished truth" is that Trump "wants to testify" because "he believes he's innocent". "And he has no need to do it, he's done nothing wrong", he stated.
Among those who have pleaded guilty are former Trump national security adviser Michael Flynn and Rick Gates, a longtime business partner of Paul Manafort, the former Trump campaign chairman who has been indicted in the investigation. Part of the investigation includes whether Trump tried to obstruct justice in the federal probe of Russian efforts to interfere in the 2016 US presidential election.
Because the president's power is contained in the Constitution, it is part of the system.