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Donald Trump has come out swinging this morning, insisting the lurid claims in the Watersportsgate dossier are "fake news".

Specifically, he took to Twitter to claim Russia had "never tried to use leverage" over him - insisting he had "nothing to do with Russia. No loans. No deals. No nothing."

If only there were some way for the President elect to prove conclusively that he has nothing to do with Russia.

Some document, perhaps, that he could publish.

Maybe something that every major presidential candidate in the last 48 years has published.

That's right...

He could release his tax returns

People have been calling for Trump to release his tax returns since almost the second he announced his run for office.

He released a 104-page "financial disclosure" shortly after his campaign launch, which details many of his jobs, directorships and income.

But financial experts say the 12,000 page tax return would contain a great amount of detail about ties with foreign governments and institutions that wouldn't be in the shorter federal disclosure form.

Every major presidential candidate since Richard Nixon has published their long-form tax return before election day.

So why hasn't Donald Trump published his tax return?

Well, he's repeatedly promised he would publish them.

In February 2015, he told a Conservative radio station: "I would release tax returns. I have no objection to certainly showing tax returns."

In January 2016, he told MSNBC: "We're working on that now. I have big returns, as you know, and I have everything all approved and very beautiful and we'll be working that over in the next period of time."

In May, when he'd been confirmed as the Republican candidate, he told Fox News: "So, the answer is, I'll release. Hopefully before the election I'll release. And I'd like to release."

He explained the delay in publication was due to the US Internal Revenue Service (IRS).

In July, his campaign chairman said: "Mr. Trump has said that his taxes are under audit and he will not be releasing them."

Does being audited prevent him from releasing his tax return?

No.

In February 2016, IRS Commissioner John Koskinen said: "From our standpoint, if you’re being audited, and you want to do something else, share that information with your returns, you can do that."

What will they reveal?

It's hard to say, because we don't know what's in them.

They could reveal funding for Trump's largely self-financed presidential campaign came via Russian oligarchs.

They could reveal he has loans or other debt linked to Russian businesses or government actors.

Or they could simply reveal that the Donald isn't quite as wealthy as he likes to make out.

But if none of the above are true - it's the only way to prove it conclusively.