President Obama scored a victory this week when Pfizer scrapped a $160-billion overseas deal that would have kept a chunk of the drugmaker's profits beyond the U.S. tax man's reach. But recent, aggressive federal actions that discouraged Pfizer Inc.'s combination with another drugmaker, Allergan PLC, won't stop all so-called inversions, or deals that end with a company relocating to another country - at least on paper - and trimming its U.S. tax bill in the process.