The secret sauce of Trump's real-estate business in its early stages was his ability to manipulate the media and willingness to borrow massive sums and not pay them back. When he exhausted his ability to stiff his creditors, the new secret sauce became a willingness to take money from shady overseas sources, especially (but not exclusively) Russian oligarchs looking either to park their cash overseas, or to gain some measure of influence. Whether Russia was investing in Trump for the purpose of gaining some hidden leverage over him is not incidental to the Mueller investigation but its very heart.