We don't know exactly how much Donald Trump paid in taxes last year. He hasn't released his 2015 federal income tax return yet. He most likely never will.
But let's keep in mind that we don't actually know how much any individual American billionaire paid in taxes last year, with just one exception. Investor Warren Buffett last month released his own basic tax info as a protest of sorts against candidate Trump.
No other billionaires followed Buffett's lead, and, under U.S. law, none of these ultra rich have an obligation to share any personal tax data at all. So we have no clue how much tax avoiding our individual billionaires are doing.
We do, on the other hand, have a sense of just how much our billionaires as a group are shelling out at tax time. Give credit for that to statisticians at the IRS. Over recent years, they've been publishing annual reports on America's 400 highest-income tax returns.
In 2013, the most recent of these reports reveals, our top 400 averaged an amazing $265 million in income -- and paid, on average, just under 23 percent of that in federal income tax.
Some of the top 400 billionaires fared far better than that average. Forty-three of them paid less than 15 percent of their reported incomes in federal tax. On paper, remember, rich couples in 2015 faced a 39.6 percent tax rate on ordinary income over $464,850.
What explains the gap between that 39.6 percent and the much lower actual tax rate on rich people's incomes? In a word, loopholes. The rich play all sorts of games -- some just a little shady, some a lot -- to get their effective tax rate down as low as possible.
If the next President of the United States really wanted to undo this "rigged" tax status quo and narrow the gap between what the law says rich elites should pay in taxes and what they do pay, what steps could that President take?
That next President, suggests a new report out of the UK, could start by assigning America's super rich their own personal tax collectors. That's just what they're doing in Britain right now, in a special tax compliance project that UK tax officials launched in 2009.
Her Majesty's Revenue & Customs, the British counterpart to America's IRS, has identified 6,500 UK taxpayers worth over £20 million -- the equivalent of about $25 million in the United States -- and matched each of these "high net worth individuals" with a HMRC "customer relationship manager."
These personal tax collectors operate as half tax cop and half concierge. Wearing the concierge cap, the customer relationship managers try to be helpful as possible to wealthy taxpayers. They'll readily answer, for instance, any question a wealthy taxpayer may have about a legally questionable tax-related move the taxpayer might be thinking of making.
As tax cops, customer relationship managers are constantly looking the shoulder of the individual wealthy taxpayers they're monitoring, watching out for fraud and any attempt to fudge income and tax-due figures.
HMRC has wisely built into this intense monitoring effort a series of safeguards to prevent what good-government analysts in the United States call "regulatory capture," the situations that develop when regulators get too close to the regulated and start ignoring the public interest.
Among these safeguards: HMRC regularly rotates the customer relationship managers assigned to each super wealthy taxpayer. And individual relationship managers don't get to make the final call on whether to pursue tax fraud investigations or not.
What sort of impact is this new British crackdown on wealthy taxpayers having? In 2015, the UK's 6,500 richest taxpayers voluntarily declared tax liabilities of £4.3 billion, about $5.3 billion. The compliance work of the HMRC special tax monitors assigned to the wealthy has already recovered another £416 million from these same super rich.
British tax officials have also identified -- and are going after -- another £1.9 billion that the super rich should have paid in taxes over recent years but haven't.
In other words, the dust could settle with the British super rich paying 35 percent more of their income in taxes than they initially expected to pay.
In the United States, collecting 35 percent more in taxes from the nation's richest would in 2013 have brought in an impressive $8.5 billion in new revenue from just 400 taxpayers.
Only one other nation -- the Netherlands -- now has a system in place that mirrors what British tax officials are doing, and this Dutch effort has only just begun.
America's IRS does, to be sure, have a unit that concentrates on taxpayers of high net worth. But the United States hasn't yet given these high-end taxpayers anything near the level of across-the-board scrutiny that Britain's HMRC has.
Could that situation change? Our top tax officials should take a look at the new report on the UK approach released earlier this month by Britain's National Audit Office. The report offers powerful evidence that placing the tax affairs of all a nation's ultra-rich taxpayers under the microscope can yield significant benefits.
How significant? UK auditors have calculated the British tax authorities gain £29 for every £1 they spend on staffers who do their agency's microscoping.
That sounds like a great deal, for both the national treasury and average taxpayers. Just by coincidence, we do have an expert deal maker about to take up occupancy in the White House. Will he try cutting a tax deal like Britain's? He would if he asked his voters.