The journalist who bared Donald Trump's 2005 taxes returns on "The Rachel Maddow Show" says Americans need to see decades of his past returns to learn "not only if their president is a crook but whether he is disloyal, can be leveraged by foreign interests or be bribed by them."

"The obvious question is: what is he hiding? Plenty," David Cay Johnston, Trump biographer and Pulitzer prize-winning investigative reporter, writes in an opinion piece in Wednesday's Guardian newspaper.

"Without his complete tax returns since the 1970s, we have no way of knowing whether he is a crook or compromised by his extensive dealings with Russian oligarchs; with authoritarian regimes in Azerbaijan, the Philippines and Turkey; or by massive loans from a bank owned by the Chinese government and the Trump Tower space rented by its largest tenant, Industrial & Commercial Bank of China."

As well, Johnston says, "Trump spent years in court fighting to not pay undocumented immigrants their $4 an hour pay. He refused to pay small business vendors over years too, putting many out of business. Lawsuits accuse him of swindling investors from Hawaii to Mexico to Florida. Are these the signs of an honest businessman?"