Washington Post reporter David Fahrenthold last year won the Pulitzer Prize for uncovering President Donald Trump's virtually nonexistent record of charitable giving -- despite the fact that Trump had boasted of giving away millions of dollars to charitable causes.

Now Fahrenthold is taking a deep look at Trump's personal business dealings, starting with Trump's decision to buy $400 million worth of real estate via cash-only transactions.

The fact that Trump last decade shifted from buying properties by taking on debt to buying properties with cash raises some red flags, as it's highly unusual for most top real estate developers to use nothing but cash to acquire new assets.

Writing on Twitter, Fahrenthold on Monday listed four burning questions that we need to have answered about Trump's sudden switch to all-cash real estate deals -- check them all out below.

The New York Times reported this past weekend that longtime Trump attorney Michael Cohen over the past decade had also built himself a real estate empire using cash-only transactions -- transactions that Richard K. Gordon, director of the Financial Integrity Institute at Case Western Reserve University’s law school, said should raise red flags over potential money laundering.