A reminder to Transportation Secretary Stephanie Pollack: The Massachusetts Constitution created three coequal branches of government. Those who ignore that sometimes inconvenient fact do so at their political peril.

The Legislature’s Transportation Committee requested the presence of seven individuals for their Monday oversight hearing into the debacle that is the Registry of Motor Vehicles. They got instead three — Pollack, Acting Registrar of Motor Vehicles Jamey Tesler, and a representative from the audit firm Grant Thornton. And Pollack made it clear she and Tesler would be limited in what they would say about events leading up to the discovery of tens of thousands of out-of-state notifications stashed in 53 bins at the RMV Quincy warehouse.

“We are trying to avoid any inquiries today that might undermine the accuracy of Grant Thornton’s ability to develop a complete and detailed timeline and assessment,’’ Pollack told the committee.

It was an exercise in executive obfuscation met with an appropriate legislative harrumph and an abrupt adjournment.

The RMV scandal was unearthed in the wake of a June crash in which a Massachusetts truck driver, whose license should have been suspended, was charged with killing seven motorcyclists in New Hampshire.

Volodymyr Zhukovskyy, who was charged with driving under the influence in Connecticut on May 11, was still behind the wheel of a commercial truck on June 21. Not surprisingly, legislators would like to know why and how that happened — and how things went so far astray at the Registry. Oversight is, after all, among the functions assigned to lawmakers.

Now to Pollack’s credit, among the first acts of the Baker administration was to call in a forensic auditing team from Grant Thornton. Presumably their work would determine how it came to be that in March 2018, when a new computer system was installed, out-of-state warnings about driver violations were simply warehoused. But that audit is not expected to be completed until mid-September.

In the meantime the audit has become an all-too-convenient dodge for Pollack.

But the idea that the existence of an audit somehow precludes testimony is nonsense. Grant Thornton is merely an auditing firm; it’s not a grand jury. In fact, there would be enormous value in having those who were closest to the situation testifying in public. After all, among the no-shows was now former-registrar Erin Devaney, whose resignation, while entirely appropriate, surely doesn’t relieve her of responsibility to tell what she knows.

Also critical to any investigation is the testimony of Merit Rating Bureau Director Thomas Bowes, who we now know remained in London even as other Registry personnel were “working day and night’’ to sift through the mounds of previously unprocessed paperwork. And we know Bowes was traipsing around London because he announced it on the campaign Facebook page set up to advance his campaign for mayor of Braintree.

Also absent was director of the RMV’s Driver Control Unit, Keith Constantino.

Pollack told the committee ahead of time that she “would not direct or prohibit any party from attending.’’ Apparently two current and one former employee took that as permission to ignore the oversight hearing.

That also caused Robert DeLeo, the usually amiable House speaker, to issue an angry statement calling on the Baker administration “to participate in the committee’s fact-finding process without exception or qualification. The Legislature will not be thwarted in the discharge of its oversight responsibilities.’’

Governor Charlie Baker, the R after his name notwithstanding, has led a rather charmed life with Democratic lawmakers, in large part because he was always viewed as a stand-up guy, honest and respectful of their needs. The current bunker mentality is unworthy of him and of his transportation secretary. His administration never had qualms about touting good news at the RMV when it reduced wait times. Now it needs to own the agency’s mishaps too.

Legislators do have one powerful option — and they shouldn’t hesitate to use it. The House and Senate Post-Audit and Oversight committees are the only legislative committees with subpoena power, and there’s nothing to prohibit a joint meeting with the Transportation Committee.

The RMV’s dirty laundry needs a thorough public airing and lawmakers are well within their right to do so on their own timetable.