Despite the President's vexation at Mueller's investigation into possible ties between his campaign and Russia -- as well as the possibility that Mueller could pursue obstruction of justice charges against him personally -- Trump has not learned that the best way to slow Mueller down is to stop making the case for him.
The basis for any investigation into a potential obstruction of justice case, as it stands now, lies primarily with the President's firing of former FBI Director James Comey. However, that in and of itself is not a crime. What Mueller would need to prove if he ends up bringing a charge of obstruction is that the President acted with "corrupt" intent. That is, Mueller would have to find evidence
the defendant "acted, at least in part ... with the purpose of accomplishing ... an unlawful end result."
In other words, Mueller would have to find that the reasons behind Trump's efforts to end the Russia investigation were ones he knew were wrong. Finding evidence of a defendant's state of mind is usually difficult, since the contents of thoughts are not ordinarily on display, and even federal prosecutors aren't mind readers.
This is where Trump's involvement in drafting Don Jr.'s statement comes into play. You see, a big problem for Mueller if he tries to prove obstruction of justice is that, well, Trump is the President. As such, he in theory has several constitutionally permissible reasons for firing Comey.
One is because he can. As the head of the executive branch, the President has the right to hire and fire the heads of the agencies he leads, just because he thinks they aren't doing a good job. Another reason he could potentially claim he fired Comey -- though this gets a little trickier
-- is because he was interfering with Trump's foreign policy goals, like improving relations with Russia, since foreign policy is an area in which the President has almost exclusive discretion
Basically, Trump's desire to get rid of Comey, or even his acknowledgment that he wants the Russia investigation to end, wouldn't on their own help Mueller meet the very high burden that Trump was actually trying to cover up something for an illegal reason.
Sarah Huckabee Sanders' admission
Tuesday that the President "weighed in" on crafting Don Jr.'s statement, "as any father would," would help Mueller in making such a case. Even if the President helped create the inaccurate statement merely to help his son avoid legal trouble, it at the very least suggests a very personal reason that Trump wanted the Russia investigation to disappear.
It also raises additional questions about how much the President knew about that meeting, or subsequent meetings, with Russian officials -- all of which could increase the scope of Mueller's investigation and give him even greater latitude to question members of Trump's staff, and even Trump himself.
Although it may be true that no parent wants to see their child get into trouble, that is unfortunately (for Trump) not a legally permissible reason to try to impede an investigation. President Trump, even if he personally had no ties to Russia, has just given Mueller a boost in potentially building a case that Trump fired Comey to conceal his family's involvement with Russia during the campaign.
When it comes to the Russia investigation, President Trump would be wise to review Scandal 101: Plausible deniability is your friend. Ronald Reagan used this premise to distance himself from the people involved and successfully avoid being implicated in the Iran-Contra affair.
Whatever the merits of the underlying Russia investigation, any obstruction case that Mueller might build is entirely of the President's own making, and Trump continues to create evidence for the case in real time. If he really wants to stop Mueller, the best thing he can do is stop being a witness against himself.