The interviews with White House staffers who were aboard Air Force One have not begun, the sources said. They currently involve only a small number of people, but the sources cautioned that number could increase. At this time, Mueller has not asked to interview President Trump. Trump Jr. was on the Hill Thursday for an interview with the Senate Judiciary Committee.

Trump Jr.’s session before the Senate Judiciary Committee included a statement centered on the most brazen, jaw-dropping excuse in a set of excuses already brazen enough to address the national need for brass over the coming decade. According to Donald Trump Jr., the reason he responded to an offer to ...

get some official documents that incriminate Hillary Clinton as part of a Russian government program to help Donald Trump

... with the phrase “I love it,” is because he was overwhelmed by the need to determine whether or not Hillary was fit to be president.

“To the extent they had information concerning the fitness, character or qualifications of a presidential candidate, I believed that I should at least hear them out,” he said.

It wasn’t about adoption, it wasn’t about doing a favor for a friend, it wasn’t about “nothing,” and it wasn’t about “opposition research.” No. Hillary Clinton made him do it.

But then, Trump Jr. might as well say he took the meeting because he’d seen pictures of Veselnitskaya and thought she was hot. Mueller doesn’t seem interested in his excuse du jour. After all, the focus of the special counsel’s attention isn’t on son. It’s on father.

Sources previously told CNN that Trump was involved in the crafting of the statement aboard Air Force One and that he involved some of his closest aides. White House press secretary Sarah Sanders -- then the deputy press secretary -- confirmed in August that Trump "weighed in as any father would" during the drafting of the statement but declined to characterize his involvement further. Mueller considers some of the aides aboard Air Force One who helped craft the statement to be witnesses.

Mueller hasn’t yet asked to talk to either Trump, because he’s following a standard set of practices.

The former FBI director leading the probe into the Trump campaign’s possible ties to Russia is taking a page from the playbook federal prosecutors have used for decades in criminal investigations, from white-collar fraud to mob racketeering: Follow the money. Start small and work up. See who will “flip” and testify against higher-ups by pursuing charges such as tax evasion, money laundering, conspiracy and obstruction of justice.

Dear White House aides: Do you really want to take a chance that Donald Trump is going to remember you on his list of people to pardon when the time comes? He who flips first survives this thing without getting to hold up a signboard bearing an inmate identification number.