If Pfizer Escapes U.S. Taxes By Buying AstraZeneca, Will Congress Be Forced To Act?

What happens if America's largest drug company, Pfizer, and America's drug store, Walgreen's, both execute deals that mean they no longer will be domiciled in America, and as a result will pay far less in American taxes? Could mergers done for the sake of dodging taxes become a key issue in the upcoming midterm elections?