House Intelligence Committee Chairman Devin Nunes may have opened himself up to an ethics probe after divulging classified information when he acknowledged the existence of a foreign surveillance warrant during a press conference last week.

According to The Daily Beast:

Nunes’s problem lies in the arcane rules of the House of Representatives. Buried in the rules regarding the House Intelligence Committee is a section that triggers a mandatory investigation into an allegation of spilling classified information.

“The Committee on Ethics shall investigate any unauthorized disclosure of intelligence or intelligence-related information,” reads the rule. The key to this rule is the phrase, “shall investigate”—a command, rather than a mere suggestion.

“The plain wording of the rule is that the ethics committee is required to conduct such an investigation,” said Brett Kappel, an attorney that specializes in political law.

The trigger could be as simple as a complaint from a single member of the House of Representatives.

Democrats, and now Republicans, are calling for Rep. Nunes to either recuse himself from the investigation or step down as committee chair.

At this point, the longer Nunes stays involved in the investigation into Russian involvement in last year’s election the more time and fodder the Democrats and the media have to rail against Republicans and the Trump administration. At this point, Nunes should step away from the investigation to simply tamp the fire over whether the investigation is being conducted properly.