The couple accused of crashing a state dinner at the white house decline an invitation to testify before congress.Lawmakers say they're trying to get to the bottom of what happened and make sure it doesn't happen again.Fox's Brian Wilson has the latest from capitol hill.THE DIRECTOR OF THE SECRET SERVICE TAKING THE BLAME ...SAYING MISTAKES *THEY* MADE ALLOWED A D-C COUPLE TO SLIP INTO A STATE DINNER AT THE WHITE HOUSE ...WITHOUT A FORMAL INVITATION.SULLIVAN says " In our line of work we cannot afford even one mistake."THE CHAIRMAN FOR THE HOUSE HOMELAND SECURITY COMMITTEE AGREES...SAYING THERE WERE UNDENIABLE PLANNING AND EXECUTION FAILURES OF THE ENTIRE SECRET SERVICE APPARATUS.THOMPSON says: " we are all fortunate that this diplomatic celebration.. did not become a night of horror."THE INFAMOUS COUPLE -- TARIQ AND MICHAELE SALAHI -- MAINTAIN THEY BELIEVED THEY WERE INVITED TO THE EVENT ... CLAIMING THEY HAVE E-MAILS TO PROVE IT.THE SALAHI'S SAY THEY DIDN'T GET A VOICE MAIL MESSAGE THAT THEIR REQUEST WAS DENIED BECAUSE THEIR CELL PHONE BATTERY DIED.SULLIVAN WAS THE LONE WITNESS AT THURSDAY'S HEARING...EVEN THOUGH THE SALAHI'S WERE ASKED TO COME...ALONG WITH WHITE HOUSE SOCIAL SECRETARY DESIREE ROGERS.THE RANKING REPUBLICAN ON THE COMMITTEE -- REPRESENTATIVE PETER KING OF NEW YORK - ACCUSED THE WHITE HOUSE OF "STONEWALLING" FOR NOT ALLOWING ROGERS TO APPEAR AT THE HEARING.KING says "If somebody from the Social Secretary's office was standing where they've always stood in the past, the Salahis would not have gotten in."SULLIVAN says "..It would have helped."CONGRESS MAN KING HAS TALKED ABOUT A POSSIBLE SUPEONA FOR ROGERS, THE WHITE HOUSE HAS SAID SHE WON'T APPEAR, BECAUSE THEY HAVE SAID THERE ARE SEPARATION OF POWER PROTECTIONS FOR WHITE HOUSE EMPLOYEES.COMMITTEE CHAIRMAN BENNIE THOMPSON ANNOUNCED HE WOULD MOVE TO SUBPOENA THE COUPLE.WHO ARE NO THE FOCUS OF AN ONGOING CRIMINAL INVESTIGATION.IN WASHINGTON, BRIAN WILSON, FOX NEWS