Reading package lists... Done
W: An error occurred during the signature verification. The repository is not updated and the previous index files will be used. GPG error: http://repo.mongodb.org/apt/ubuntu xenial/mongodb-org/3.2 Release: The following signatures were invalid: KEYEXPIRED 1507497109
W: Failed to fetch http://repo.mongodb.org/apt/ubuntu/dists/xenial/mongodb-org/3.2/Release.gpg The following signatures were invalid: KEYEXPIRED 1507497109
W: Some index files failed to download. They have been ignored, or old ones used instead.
Essentially getting the correct key:
sudo apt-key adv --keyserver hkp://keyserver.ubuntu.com:80 --recv EA312927