Every politician wants easy ways to raise revenues. Few are more beautiful than getting money from people who are already cheating on their taxes, or are abusing tax laws to artificially reduce their taxes in unintended ways.
This international tax gap isn't part of the official tax gap measures by the I.R.S. because it is hard to measure. But, changes in international taxation could raise $50 billion or more a year, with almost no pain to legitimate taxpayers. A detailed analysis of what can be done to address the problem is set forth here.