Last week, Republican presidential candidate John McCain called for a commission to "find out what went wrong" on Wall Street. It was an excellent suggestion: Public inquiries into Wall Street practices served the country well in the 1930s.

And Mr. McCain has a special advantage to bring to any such investigation -- many of the relevant witnesses are friends or colleagues of his. In fact, he can probably get to the bottom of the whole mess just by cross-examining the people riding on his campaign bus. So the candidate should take a deep breath, remind himself that the country comes first, pull the Straight Talk Express over at a rest stop, whistle up his media pals, and begin.

Topic A should be deregulation. Financial institutions are dropping everywhere after playing with poorly regulated financial instruments; the last investment banks standing are begging the government for stricter oversight; and some of our nation's leading champions of laissez faire have ditched that theory in an extraordinary attempt to rescue the collapsing industry.

The philosophy of government that has dominated Washington for almost three decades is now in ruins, and it is up to Mr. McCain to find out exactly why we believed it in the first place. Why did government stand back and permit all the misconduct that generated all this bad debt? What particular ideas led us to believe that government should just keep its hands off and let markets run their course?

Maybe the McCain Commission on Deregulation can kick off with a statement from the candidate himself. It will be helpful for the public, if painful for the senator himself, to hear about Mr. McCain's own close brush with one of the towering figures of financial deregulation, Charles Keating, the master of Lincoln Savings and Loan. Keating had a special, urgent interest in getting Big Brother off our backs: in 1986 some meddlesome agency suspected him of massive violations of S&L regulations. Keating fought back by recruiting a handful of legislators, including Mr. McCain, to pressure S&L regulators to leave his S&L alone. A few years later, Lincoln became one of the largest financial failures in U.S. history.