First, lobbying (the technically correct term for most of the activities bought by "the millions going into Washington") is both lawful and constitutionally protected (first amendment, third clause). Bribery, for which some of it might be spent, is not protected, not lawful, sometimes prosecuted, occasionally with success.
Second, a good deal of the "billions finding their way into corporations" do, in fact, buy domestic services and supplies, pay salaries and taxes, and otherwise contribute to the general welfare. The fraction may be too small for many people's taste, but it is a rare corporation that does not spend around 80% of its gross revenue for such things. Those, like Google and Uber, that have no tangible product probably are the most notable exceptions.