The Secret Service is investigating how a couple aspiring to be reality-show celebrities managed to appear at President Obama’s first state dinner without being on the guest list, provoking questions about security at the White House.
http://www.nytimes.com/2009/11/27/us/politics/27party.html

The president didn't invite his 2008 rival, Sen. John McCain of Arizona, even though Obama the candidate pledged a post-partisan presidency.