Newsmaker: Jack Lew
Who said politicians have no power any more?
If we needed, or wanted, evidence of the awesome power of government to bend events to their will, we got it last week when the US effectively killed the largest pharmaceutical merger in history when it promised new rules on so-called "inversions".
Last Monday Allergan shares plunged 22pc after the department of the treasury - led by Mr Lew said it will impose a three-year limit on foreign companies bulking up on US assets to avoid ownership limits for a later inversion deal.
In effect, the new regulations killed off any hope of Dublin-headquartered Allergan succesfully merging with Pfizer and locating the new business in Ireland for tax purposes.
That wasn't all, though. Mr Lew said that more would be done to "further rein in" inversions. Clearly, he isn't done yet.
Historically, Mr Lew would be one of the most influential treasury secretaries in history. Except both his predecessors - Tim Geithner and Hank Paulson - have been arguably the two most influential secretaries ever. The renewed power of the treasury has been a product of the financial crash but Mr Lew has clearly retained his focus on maintaining the treasury's influence over policy.
Unlike Paulson and Geithner, Mr Lew did not have much of a public profile when he was appointed in 2013.
Bespectacled and unassuming, he spent most of his career in public service as a staffer and manager behind the scenes, preferring to avoid the limelight. He served as budget director under former President Bill Clinton as well as Barack Obama.
He is no stranger to controversy, however. During his confirmation hearing three years ago, a number of lawmakers were sharply critical of the large bonuses and other perks he received from previous employers Citigroup and New York University.
Mr Lew was also grilled about an investment he once had in the Cayman Islands. In his 2008 presidential campaign, Obama criticised the practice of using the Cayman Islands as a tax haven.
Barack Obama's presidency is heading steadily towards lame duck territory ahead of November's presidential election. It is clear though that, for now at least, Mr Lew isn't content to just see out what remains of the administration's term. (Additional reporting by Reuters)