NBC News’ Kristen Welker reported via Twitter Friday afternoon that “Secret Service Director Mark Sullivan will announce his resignation today according to multiple sources.” Sullivan has overseen the Secret Service since 2006 and was its director during the agency’s high-profile prostitution scandal last year. 12 Secret Service agents and several other military personnel were allegedly involved with prostitutes in Cartagena, Colombia in April 2012. Those agents were sent there to set up advance security ahead of a visit by President Obama.