House Democrats will 'undoubtedly' find the president has committed multiple crimes: Trump biographer
President Donald Trump. (AFP / Mandel Ngan)

David Cay Johnston, an investigative reporter who has written extensively about President Donald Trump's finances, told CNN on Monday that Democrats in the House of Representatives will find a treasure trove of evidence that the president is a criminal.

When asked by CNN's Alisyn Camerota about the importance of obtaining the president's tax returns, Johnston said that those records would only be the first of many avenues Democrats could use to probe Trump's finances.

"The tax returns are the beginning point to look at Trump's connections," Johnston explained. "But in addition to that, wire transfers are all searchable. Every single transaction where Saudi money, Russian money, any other dubious transactions took place, those can all be found and identified."

Johnston then recounted some of the past financial shenanigans that the president had engaged in dating back to the 1980s -- and he said overturning just a few stones should be enough to show Trump has regularly broken the law.

"We're going to absolutely see that Donald has done things that are illegal," he said. "Remember, this is a man whose own tax lawyer -- when Donald had one of his civil trials for income tax fraud -- testified, 'That's my signature but neither I nor my firm prepared that tax return.' Somebody who will go that far in committing fraud is undoubtedly going to be uncovered in this investigations."

Watch the video below.