Treasury Secretary Jacob Lew announced Monday night that he would begin cracking down on American companies that avoid taxes by moving their headquarters overseas. Lew will stop these so-called “tax inversions” by making it more difficult for smaller foreign companies to take over larger U.S. companies, and by making “hopscotch” loans—where U.S. companies get around paying taxes on dividends by distributing earnings as a loan to a foreign company—taxable.