Mueller report: Here's what we know and still don't know (and may never know)

The world got its first glimpse on Sunday into the investigation that has cast a cloud over Donald Trump's presidency.

After two days reading through Special Counsel Robert Mueller's confidential report, Attorney General William Barr sent a letter to Congress offering a summary of the investigation into Russian interference in the 2016 presidential election and possible links to Trump's campaign.

In Barr's letter, he said that no proof was found that the Trump campaign conspired with Russia but said no decision was made over whether the president obstructed...