While Republicans and some others insist that President Obama is a lame duck and in the twilight of his presidency, he is still showing that his office exercises considerable muscle and power in order to work on the behalf of taxpayers.This time it was a victory against the big pockets of Big Pharma, who were attempting a corporate maneuver that would allow them to skip out on a big part of the tax bill they owe America.Pfizer has announced that its planned merger with Allergan will no longer go through. As CNBC reporter David Faber noted in a tweet,  Changes in inversion regs dealt deal death blow. Pfizer and Allergan will mutually terminate their merger tomorrow morning- sources.Changes in inversion regs dealt deal death blow.$AGN,$PFE  David Faber (@davidfaber) April 6, 2016That decision came just a few hours after President Obama announced that his Treasury Department would release new rules that allowed the government to crack down on so-called corporate inversions, a maneuver that allows companies to effectively dodge paying taxes:Inversion is when a company moves its tax residence overseas on paper, typically to a low-tax country, to avoid paying their fair share in taxes here at home.When multinational corporations exploit these loopholes   enjoying the many benefits of locating in the United States without responsibly paying into the system   it erodes the American tax base, undercuts businesses that play by the rules and ultimately leaves the middle class and small businesses to pay the tab.The $150 billion proposed deal between Pfizer and Allergan came directly in the sights of these new Treasury rules, and as the L.A. Times reported,  the Treasury Department seemed to be targeting the Pfizer-Allergan deal and others like it. As has often been the case, President Obama has had to use the power of his office to go after activities like this because the Republican-controlled Congress has spent more time sitting on their hands than actually doing anything. He again implored Congress to address inversions, and noted,  When companies exploit loopholes like this, it makes it harder to invest in the things that are going to keep America s economy going strong for future generations. It sticks the rest of us with the tab. And it makes hardworking Americans feel like the deck is stacked against them. Despite GOP wishes, Obama hasn t hung it up yet, and another bunch of pharma bros are feeling it.Featured image via YouTube screen capture