Senate Judiciary Committee chairman Charles Grassley and the committee's ranking Democrat, Dianne Feinstein, want to interview two high-ranking FBI officials about some key aspects of the bureau's role in the Trump-Russia investigation -- the Trump dossier, the firing of James Comey, and more. But the FBI doesn't want those officials to talk -- even though the Judiciary Committee has oversight responsibility for the FBI, and even though the request is bipartisan, and even though there appears to be no conflict with the ongoing Trump-Russia investigation conducted by special prosecutor Robert Mueller.

A standoff could be developing.

It began on July 11, when Grassley and Feinstein wrote letters to James Rybicki, who was Director Comey's chief of staff, and Carl Ghattas, head of the bureau's national security branch. "The committee is investigating the removal of FBI Director James Comey, Russian interference in the 2016 election, and allegations of improper interference in law enforcement investigations," the chairman and ranking member wrote. "Please make yourself available for a transcribed interview during the week of July 24, 2017."

It didn't happen. On July 27, Samuel Ramer, the acting assistant attorney general, wrote to say that Rybicki and Ghattas would not be talking. Noting the Mueller investigation, Ramer said, "Under these circumstances and consistent with the department's long-standing policy regarding the confidentiality and sensitivity of information relating to pending matters, the department cannot make Mr. Ghattas or Mr. Rybicki available for transcribed interviews at this time."

Grassley and Feinstein did not agree. They knew that committee staff, Republican and Democrat, had had so-called "de-confliction" discussions with Mueller's office on how the Senate investigation might proceed without interfering with Mueller's criminal probe. And they didn't see a conflict. So on August 25, Grassley and Feinstein wrote another letter, this time to Deputy Attorney General Rod Rosenstein.

"The department declined to make Mr. Ghattas and Mr. Rybicki available for interviews because of pending matters and their current work on those matters with Special Counsel Robert Mueller," Grassley and Feinstein wrote. "However, in our de-confliction discussions with the Special Counsel's office, we have clarified that the committee intends to limit the scope of the interviews to avoid that concern. There is no intent to seek information about these witnesses' current work with the Special Counsel's office. Rather, we seek their independent recollections, as fact witnesses, of events that occurred before and including Director Comey's removal."

The two lawmakers asked the Justice Department to get in touch by September 1 to schedule the interviews. "We appreciate and expect the department's voluntary cooperation with this important request," they wrote.

Including the words "expect" and "voluntary" was notable, because it essentially meant, "Don't make us force you." If they are united, the chair and the ranking minority of a Senate committee can make a lot of trouble for an agency under their oversight. Grassley and Feinstein, veterans of many years in the Senate, know that very well.

The Justice Department does, too. But September 1 came and went with no department effort to set up the interviews.

Now, it is not clear what is next. Grassley and Feinstein appear to be determined to talk to Rybicki and Ghattas. It is obvious that both men know a lot about what went on in the FBI in the last couple of years. As far as the Trump dossier specifically is concerned, they could be able to shed light on the FBI's reported decision in October 2016 to support work on the dossier, which at the time was an anti-Trump opposition research project funded by Clinton donors. Grassley has said that decision "raises further questions about the FBI's independence from politics." There's no doubt he wants to learn more about it.

Finally, sharp-eyed readers may have noticed the name of James Rybicki in the news in the last few days. He was one of the FBI officials cited in a letter from Grassley and Republican Sen. Lindsey Graham suggesting that Comey may have decided to exonerate Hillary Clinton in the email investigation before Clinton and more than a dozen other witnesses were even interviewed. The senators based the charge on Rybicki's interview with the Justice Department's Office of Special Counsel. (They took care to note that, despite the name, the Office of Special Counsel is completely separate from and not related to the Robert Mueller investigation.) Rybicki, as Comey's chief of staff, obviously knew a lot about the email investigation.

Now Grassley and Feinstein want to know what Rybicki, as well as Ghattas, knows about the dossier, the Comey firing, and other events that make up the broadest definition of the Trump-Russia affair. But first, they'll have to get past the Justice Department's determination to keep things secret.