Johnston appeared on MSNBC on Tuesday night to report on the document, which he says was delivered anonymously to his mailbox. He speculated that Trump — the first president in decades not to release his tax returns — or someone close to him was the source.
The White House issued a statement to ABC News before the broadcast, lauding Trump's income and taxes paid.
"Before being elected president, Mr. Trump was one of the most successful businessmen in the world, with a responsibility to his company, his family and his employees to pay no more tax than legally required," the statement read. "That being said, Mr. Trump paid $38 million dollars even after taking into account large scale depreciation for construction, on an income of more than $150 million dollars, as well as paying tens of millions of dollars in other taxes, such as sales and excise taxes and employment taxes, and this illegally published return proves just that."
It's not clear where the document originated. Johnston defended himself to MSNBC's Rachel Maddow, saying it's within his First Amendment rights to publish documents that were delivered to him. "By the way, let me point out that it's entirely possible that Donald sent this to me," Johnston said. "Donald Trump has over the year leaked all sorts of things." The two-page document, which Johnston produced, is stamped with the words "client copy" on the second page.
The document shows Trump declared $103 million in losses in 2005, and his effective tax rate of 25 percent placed him well under the top rate of 35 percent. However, that rate is much higher than the 14 percent that Mitt Romney paid the year before he was the Republican presidential nominee.
It's notable that Trump paid income tax at all in 2005. Although he has refused to discuss his income tax rate or release his returns, The New York Times reported last year that his 1995 tax return showed Trump took a $916 million loss, which the paper said "would have been large enough to wipe out more than $50 million a year in taxable income over 18 years."
Trump is the first president since Richard Nixon to refuse to release his full income tax returns. During a January press conference, Trump was asked if he would release them in order to prove that he has no dealings or debts with Russia.
"I'm not releasing the tax returns," he said, "because, as you know, they're under audit."
Trump denied having any dealings with Russia and said, "The only one that cares about my tax returns are the reporters, OK? They're the only who ask."
And in an interview with ABC's "This Week" in January, counselor to the president Kellyanne Conway told George Stephanopoulos, "The White House response is that he's not going to release his tax returns. We litigated this all through the election. People didn't care."