Three additional Secret Service agents quit the force over scandal
President personally briefed on state of the investigation
Questions over whether agents slept with underage girls
Colombian prostitute at the hear of affair has gone into hiding
Says she was eventually paid $225 for the evening
Claims to fear retaliation by the U.S. government
The prostitution scandal which has devastated the Secret Service could be set to spread to the White House.
A senior Republican has urged [...]