This is what happens when former presidents discover hashtags.
Bill Clinton Tweeted a thank you to George W. Bush Wedesday for receiving a copy of his new book, "41," with the hashtag: HowAreYouSTILLNotOnTwitter.
Then Bush replied with an Instagram, screenshotting Clinton's tweet and adding his own special hashtag in the comments: BrotherFromAnotherMother.
Still waiting on Obama's response via Vine.