The FEC, in a letter to CREW, said it dismissed the complaint because the issue comes down to Ensign's parents' intent in giving the money: i.e., whether it was a personal gift or a contribution. Ensign's parents gave the FEC sworn affidavits saying it was a gift.
"As a practical matter, it is doubtful that an investigation would produce any additional evidence that would contradict or outweigh this testimony," the FEC wrote. "Accordingly, we conclude that an investigation in this matter is unwarranted and would not be an efficient use of Commission resources."
You can read the whole letter here.
Ensign is still reportedly being investigated by both the Justice Department and the Senate Ethics Committee for other potential misconduct resulting from the affair he had with his staffer, Cynthia Hampton. He recently announced that he will run for re-election in 2012.
Ensign, TPM readers will remember, admitted in 2009 to having an affair with Hampton. Hampton's husband, Doug, was also a senior staffer and close friend of Ensign. After the affair, the couple left Ensign's employ and Ensign allegedly helped Doug Hampton get a lobbying job and clients -- a potential violation of the one-year Senate lobbying ban. Ensign's parents also gave a total of $96,000 to the Hampton family.
Find many, many more details of the affair here.