My assumption from Herridge's account is that Pientka is cooperating with the Senate investigators voluntarily--unlike former head of FBI counterintelligence, Bill Priestap, who will only appear if subpoenaed. My takeaway from this is that it almost certainly means that Pientka has already cooperated fully with both IG Horowitz's FISA related investigation as well as with John Durham's more wide ranging investigation. Signs have, IMO, always pointed in that direction--it has long been apparent that Pientka disagreed with the framing of Flynn and, in the wake of that "awakening," may have realized the full scope of the Russia Hoax.
Thus, I assume that Pientka's period of cooperation with the Durham investigation is now complete and Pientka has been made available to the two Senate committees. More to the point, this almost certainly also means that Durham believes he has no further need to keep Pientka's cooperation confidential--Pientka's cooperation has already been put to whatever use it could have for investigative purposes. And that's another sign that an important phase of Durham's investigation--the pre-inauguration phase--is drawing to a close. A fact that disgraced former FBI Director James Comey is, no doubt, painfully aware of.
Herridge (edited only to form a continuous narrative):
SCOOP: Two sources close to the Senate probe tell @CBSNews that FBI agent Joe Pientka has been interviewed behind closed doors for "multiple hours" by investigators with Senate Judiciary + Senate Oversight/Governmental Affairs.
In 2018, then-Chairman @ChuckGrassley first sought Pientka's testimony but the request was denied until now.
WHY IT MATTERS: Pientka is at the intersection of key events in the #Durham investigation. Along with agent Peter Strzok, Pientka conducted the January 2017 WH interview of @GenFlynn that led to [Flynn's] dismissal.
More recently, declassified records showed Pientka + others used an August 2016 "defensive-briefing" to warn candidate Trump, Flynn + @GovChristie about national security threats to gather information on their line of questioning about Russia for the FBI probe known as Crossfire Hurricane. These events + decision making fall under Durham.
Note the awkward phrasing of the final paragraph. What Herridge means is that Pientka--at the direction of Strzok and Strzok's superiors and fellow coup plotters, used what was supposed to be a standard national security briefing for candidate Trump to conduct "personality assessment" on both Trump and Michael Flynn, with a view to preparing for later investigative events, i.e., interviews. In other words, the FBI was consciously targeting both under the pretext of conducting a national security briefing in order to develop a line of questioning to be used in later interviews.
When Herridge notes that "Pientka is at the intersection of key events in the #Durham investigation" I believe that she's pointing to Pientka's involvement in:
* The opening of Crossfire Hurricane;
* The FISA targeting Carter Page;
* The use of DoJ official Bruce Ohr as a conduit for the continued use of formally terminated confidential source and MI6 officer Chris Steele;
* The Flynn interview and later prosecution--with focus on Pientka's participation in the interview and the production of the FD-302 for the interview of Flynn.
Lots there to justify "multiple hours" of questioning by Senate investigators. I'm sure Durham's investigative interviews of Pientka ran to multiple days, if not weeks.