The news that President Trump’s legal team is already evaluating the scope of his pardon authority, as well as steps that can be taken to push back on the breadth of Special Counsel Robert Mueller’s investigation, rippled across social media Thursday night.

Of particular interest was that Mueller’s potential inquiry into the president’s financial dealings (and his tax returns) has apparently so incensed President Trump and resulted in a warning that the former FBI director should not cross that proverbial “red line.”

President Trump, of course, has a long history of being a more-than-capable litigant in his pre-presidential life, and he certainly is not a newcomer to the legal game. His battles with Eric Schneiderman, for instance, were legendary—at one point, Trump even filed a complaint about the New York attorney general with the state’s ethics commission. In 2010, he used civil litigation to effectively persuade Deutsche Bank (and other lenders) to grant him an extension on a $640 million construction loan.