Facebook and YouTube are blocking references to the alleged identity of the Ukraine whistleblower, the Washington Post reports.

Driving the news: Donald Trump Jr. shared the whistleblower's supposed name on Twitter. President Trump has said the whistleblower's identity "must" be determined after details of their complaint have been examined in an impeachment inquiry.

Twitter said it would permit references to the whistleblower on its app, including in posts shared by Trump supporters that include the alleged name and photos.

to the whistleblower on its app, including in posts shared by Trump supporters that include the alleged name and photos. The whistleblower's lawyers sent the White House a "cease and desist" letter this week over Trump's calls for the whistleblower's identity to be made public.

The big picture: Facebook's current political ad policy allows politicians to repeat false claims or misstate an opponent's record or their own. Facebook has already begin removing the whistleblower's name from posts "for a few days," AP reports, and will revisit its decision if the name surfaces in public debate or is circulated in the mainstream media.

Between the lines: Social media platforms are largely left to their own devices when it comes to creating rules on speech and content — allowing for gaps and inconsistencies as they build guidelines where federal and state parameters are lacking.

Go deeper: Facebook, Google weigh changing political ad policies under pressure