Trump's net worth may be more than a billion on paper, but at some point in the mid to late 2000's he was in a cash squeeze. Despite huge equity in real estate holdings, he didn't have enough cash flow.
The value of his brand required constant renourishment. The minute he would try to sell equity in real estate deals to raise cash, his brand would lose value and the whole house of cards would fall. If the value of the Trump brand is damaged, the loans get called. Trump had been there, before.
In the 1980's, Donald Trump survived a well-documented high wire act with bankruptcy. His failed airline. His failed casino in Atlantic City. Then, lenders rescued Trump from bankruptcy, because they needed Trump's salesmanship to salvage their equity. It took a while, but at some point Trump broke off leash.
By the late 00's, according to this theory, Trump got over-leveraged a second time. He had to borrow, but he couldn't cobble enough from lenders who had already been burned by him once.
No one in the U.S. would loan Trump enough money to keep the brand inflating – he had already screwed everyone in the debt markets. Plus he couldn't afford the risk to his brand from a whisper campaign by the bankers.
So Trump went offshore, to the Russians. Quiet, dirty money before he decided to run for president, a venture whose first purpose was to shine his brand even more brightly.
He met a few oligarchs along the way to crowning Miss Universe in Moscow where he was probably caught on tape. They introduced him to Russian bankers indifferent to dirty money. And in rescuing Trump from a liquidity crisis, they cushioned his run for the presidency that no one thought he would win but served Putin's long-standing interest in damaging the credibility of the United States.
For the Russians, the investment in Trump was meant at first to disrupt Hillary, hence Wikileaks. That intervention had plenty of help from Fox and the Rupert Murdoch empire.
Trump will never release his tax returns voluntarily because the details embedded in the return document the cash squeeze and lenders tied to the Russian oligarchs and Putin.
Trump's returns would also show his welching on charitable contributions like to the vets, his needing to raise money for the campaign despite being "a billionaire”, and why his campaign against Hillary was so "cost effective".
Donald Trump ran the biggest political con in American history, that would not have been possible without dirty money from Russia, and no one called him on it. Not the American voters in three key states, totaling less than 100,000, that delivered the electoral college. Not the GOP Congress whose leaders will be forever tarnished if this theory holds.
Don't get bogged down in the Russian hack story. The big theory is that the president of the United States is owned by Russia, and that all the little lies add up to impeachable offenses.