former secretary of state is expected to announce candidacy sunday afternoon and then hit the campaign trail .
iowa sources say democrats are preparing for hillary to barnstorm the state sunday and monday .
social media posts will be followed by video and email announcements .
new polls suggests the former first lady is slipping behind leading 2016 republican candidates in vital swing states .
new epilogue of her book ` hard choices ' reveals how becoming a grandmother inspired her to run for president .
republicans launch ` stop hillary ' ad campaign .