Donald Trump always talked a lot about how much money he's donated to charity over the years. The self-proclaimed billionaire says he's given away “millions”; and his former campaign manager, Corey Lewandowski, put the total at “over $100 million.”

But when The Washington Post's David A. Fahrenthold tried to prove him right, and track where that money went, it proved more difficult than he expected.

Inside The Post's investigation of Donald Trump's charitable giving (Peter Stevenson, Julio Negron/The Washington Post)

“A lot of other wealthy people feel the responsibility to take some of the wealth they've been given and give back,” he said in a recent chat with The Fix. “To give a lot of money to a particular cancer charity or to a group researching some particular disease or their alma mater. We haven't really found anything like that with Trump.”

But even without a go-to charity, Trump still regularly claims he gives a lot of money away. So the question became, to whom?

Fahrenthold got no help from the candidate's campaign or the Trump Organization. So he started reporting the old-fashioned way: by making a list of charities to which Trump might have donated and contacting them one at a time.

And he tracked his research using an old-fashioned tool: his notebook (yes, even in the digital age, the notebook is a critical tool for journalists).

In the video above, we explore Fahrenthold's reporting and some of what he discovered along the way.

Read some of Fahrenthold's stories: