"The fact that" is a usage made when one wants to use an important statement in order to strongly prove, disprove or establish another statement.
It's usage is limited to arguments or dramatic situations. It might sound impolite in formal settings such as email or business meetings.
A more polite way to establish something would be using "Based on" or "can be gathered".
Based on your joke about black Americans smoking weed, it can be gathered that there are preconceptions that white Americans have about black Americans.
However, do note that the logic of the above sentence does not hold good because often one needs many data points in order to prove or disprove something general. Trump's behavior is not representative of that of all white Americans, just as Obama's behavior is not representative of all black Americans.