(CNN) President Donald Trump is concerned about whether his son Donald Trump Jr. might have exposure in the special counsel's Russia investigation, leading to his increasingly frenzied public agitation over Robert Mueller, sources close to the White House tell CNN.

Trump has been concerned for months now that the Mueller probe could reach his family, and potentially his son-in-law Jared Kushner, but his focus has turned to his namesake in recent weeks, one person who speaks with Trump frequently tells CNN. This is one of several reasons Trump has upped his public attacks on Mueller, because he doesn't want him touching his family, the person adds.

Others who have been close to the President -- including his former White House communications director, Anthony Scaramucci, and former White House chief strategist Steve Bannon — have suggested the President at the very least knew shortly after the fact.

The President denied that he is worried about the Trump Tower meeting in a Twitter post Sunday morning.