The Senate Ethics Committee found that John McCain had exercised poor judgment in relation to the collapse of Lincoln Savings and Loan in 1989 and the associated scandal referred to as "Keating Five."
See Wikipedia for more background and links on the Keating Five scandal, and :
The Arizona Republic (1st March 2007): The Keating FiveThe New York Times (15 November 1990): Washington at Work; Taking On 5 Senators, Ethics Panel's Counsel Insists He's Not Political.Real Clear Politics: Transcript of Fox News interview from Hannity and Colmes with Bob Bennett, 20 February 2008.