The informal U.S. congressional probe into alleged security violations involving foreign nationals at two NASA field centers illustrates both the good and bad that can result when lawmakers, in exercising legitimate oversight responsibilities, get spun up on a particular issue. Unfortunately, in many cases, possibly including this one, the consequences are more negative than positive.

The most obvious historical example is the 1998 congressional investigation into allegations that China was gaining access to sensitive missile technology by launching U.S.-built commercial satellites. That review did in fact reveal flaws in the export control system, even if the national security implications were vastly overstated.

But the resulting crackdown on satellite exports, imposed by a law that took effect in 1999, proved damaging enough to the U.S. space industrial base to alarm even those agencies responsible for national security — to the point that they joined the chorus of calls for reform. The effects of that law are still being felt, even as the White House drafts rules to implement legislation passed in 2012 that overturns its most onerous provisions.

China is the focus of the latest probe, spearheaded by Rep. Frank Wolf (R-Va.), chairman of the House Appropriations subcommittee with NASA oversight and fierce critic of Beijing. Mr. Wolf, along with House Science Committee Chairman Rep. Lamar Smith (R-Texas), is pushing NASA to tighten enforcement of rules restricting access to agency centers and technology by foreign nationals. They also have prodded U.S. federal law enforcement authorities to take action on alleged violations of the International Traffic in Arms Regulations (ITAR), which govern exports of space technology, at NASA’s Ames and Langley research centers.

The lawmakers have found traction in one instance: FBI agents on March 16 arrested a Chinese national and former Langley contractor, Bo Jiang, at a Washington-area airport for lying about computer equipment he was carrying while boarding a plane for a one-way trip to China. According to charging papers filed by the FBI, the agency acted in part on information provided by Mr. Wolf. It is unclear at this point whether Mr. Jiang will be charged with anything other than lying to U.S. federal law enforcement authorities.

NASA, meanwhile, is reviewing its security procedures in response to Mr. Wolf’s allegations about export control violations. This is a reasonable and healthy outcome given that NASA’s centers deal in sensitive technologies and have frequent interaction with non-U.S. citizens through a variety of relationships and arrangements that are often poorly understood.

But Messrs. Wolf and Smith crossed the line in publicly suggesting that the director of Ames Research Center, Simon “Pete” Worden, turned a blind eye toward criminal conduct at the facility. That’s effectively what they did in letters sent Feb. 8 to senior U.S. Justice Department officials — and released to media — demanding information about alleged export violations at Ames. “It is our understanding that this illegal technology transfer may have involved classified Defense Department weapons system technology to foreign nations, including China, potentially with the tacit or direct approval of the center’s leadership,” the lawmakers wrote.

In that letter, and in subsequent public statements, the lawmakers provided no actual evidence that anyone broke the law; they cited anonymous “whistleblowers” and law enforcement sources. The lawmakers also suggested, again without providing evidence, that the decision not to prosecute the case, which had been the subject of a Justice Department investigation, was politically motivated. Notably, Mr. Wolf’s subcommittee also oversees Justice Department funding.

Mr. Worden, a former U.S. Air Force brigadier general known for operating outside the box of conventional thinking, denied any coverup and said the letters — and the resulting press reports — were “riddled with inaccuracies.” Melinda Haig, the U.S. attorney for the Northern District of California, meanwhile, denied the lawmakers’ assertion that her office had sought permission to prosecute the case only to be refused by higher-ups at the Justice Department.

Messrs. Wolf and Smith may have good reason to believe export violations indeed occurred at Ames. After all, under the legal-regulatory regime that was in place from 1999 to 2012, just about anything related to space — regardless of application or sophistication — could be pulled under ITAR’s umbrella.

But publicly branding Mr. Worden as a possible accessory to a crime, without presenting any evidence, was shameful. So too are the lawmakers’ attempts to bully the Justice Department into prosecuting the case.

More broadly, Mr. Wolf’s crusade threatens to create a chilling effect on all kinds of information and technology sharing activities among scientists that have never before been a source of concern. For example, as Mr. Wolf widened his inquiry, NASA closed public access to an online repository of engineering data, long used by the scientific community, pending an ITAR review that could take months, if not years.

Meanwhile, there have been at least two recent instances in which information on launch vehicle anomalies has been withheld in the name of ITAR compliance, once by NASA and once by rocket maker Space Exploration Technologies Corp. While there is no evidence that this is related to Mr. Wolf’s inquiry, one has to wonder if public disclosures that traditionally have followed failures of government rockets and spacecraft — and in some cases revealed design flaws and avoidable human error — will become a thing of the past.

Nearly 15 years after the congressionally mandated crackdown on satellite technology exports, the government is trying to reverse its unintended yet predictable consequences. The current inquiry may well reveal holes in NASA’s security system, but its shoot-first-and-ask-questions-later approach already has unfairly damaged the reputation of a high-profile agency official. It also threatens to create a climate of excess caution — if not outright fear — that could slow the momentum of ITAR reform while stifling the information exchanges that benefit NASA in the long run.