The U.S. Supreme Court has ruled that campaign donations to political candidates are a constitutionally protected form of free speech, and the Oregon Supreme Court has applied the same reasoning at the state level. That leaves disclosure as the public's chief bulwark against big donors' influence over candidates: Oregonians can't limit the amount of money flowing into campaigns, but they can at least find out where it's coming from. Oregon's primary election campaign, however, has revealed a gaping loophole in state disclosure requirements — a loophole the 2019 Legislature should close, no matter who wins today.

The loophole became visible in the contest for the Republican gubernatorial nomination. One of the leading candidates, former Navy aviator Greg Wooldridge, reported that $125,000 of his $288,000 in campaign funds came from two out-of-state corporations. Anonymous campaign contributions are prohibited in Oregon, but identifying corporate donors means little if there's no way for the public to find out who controls the corporations.

Some legwork by the Associated Press identified the person behind the larger of Wooldridge's donations: The owner of a California real estate company who shares the candidate's interest in veterans' issues gave $100,000. The source of the other $25,000, however, remains a mystery. It came from a Nevada company whose business license has been revoked. Some states have lax laws governing corporate registrations — Nevada allows corporations people who have nothing to do with the business to be listed as officers. The AP quoted The Las Vegas Sun as reporting that one person was listed as a corporate officer for 4,000 different Nevada companies.

Wooldridge's campaign is not accused of having done anything wrong. The secretary of state's office says campaigns can't be responsible for researching their contributors' backgrounds. But when a candidate's money trail leads into a corporate black box, the purpose of the law against anonymous campaign donations is defeated. Unlimited amounts of money could flow into Oregon campaigns from companies created to shield donors' identities.

Oregon can't do much about other states' business registration practices. The state could, however, impose tighter campaign donation reporting requirements on candidates and ballot measure campaigns. A candidate or campaign receiving a donation above a certain threshold — say, $2,500 — could be required to name an individual, or a group whose officers' names are public record, as the source of the money. In the absence of practical limits on campaign donations, disclosure is an important line of defense against undue influence by unseen forces.