but you know what, dont listen to what the congressman said, he probably got the wrong info, i am sure your case is fine and is ready to be sent to the nvc, uscis probably has not updated your case status on their system, and that's why they told your congressman that your case is in security checks, contact your attorney, and have your attorney contact the us attorney's office, and let the us attorney know what the status of your case, the us attorney will contact uscis and transfer your case to the nvc,i am sure by that time , your case will be at the nvc. good luck and stay positive, everything will be fine, you already got your approval from uscis, now it's time to move on to the nvc.