If you drill down into Peter Strzok’s testimony from his hearing before Congress, there are at least three issues of potential criminality that must be further investigated. From Jon Hall at fmshooter.com:

Last Thursday, embattled FBI agent Peter Strzok testified and was questioned by members of the House during a publicly broadcast hearing that spanned for more than ten hours.
Largely, the hearing was partisan posturing from both sides – with the Republicans grilling Strzok over his text messages to and from FBI mistress Lisa Page and the Democrats widely supporting and applauding Strzok’s fiery defiance.
Democratic Rep. Steve Cohen (D-TN) even went so far as to suggest Strzok deserved a purple heart for enduring the GOP’s treatment of him at the hearing.
Despite the limitless posturing – a few key questions were answered in the lengthy ten hours…
How Clinton’s charge of using a private home e-mail server went from “grossly negligent” to “extremely careless”?
Republican Rep. James Sensenbrenner (R-WI) inquired how the wording of a statement condemning Hillary Clinton’s use of a private e-mail server was changed before it was even issued.

Strzok, who led the FBI’s investigation into Hillary Clinton’s use of her personal e-mail server, rephrased the charge of Clinton’s actions from “grossly negligent” to “extremely careless” in a draft of the FBI’s statement that was publicly issued by then-FBI Director, James Comey.
However, Strzok argued that the revision was introduced by the FBI’s legal counsel, who noted that “gross negligence” carried a specific legal meaning with specific legal implications.
When Sensenbrenner asked why the change had been made, Strzok explained:
With regard to that decision, there was concern within the perspective of a legal definition of that term that people would draw an inference based on that use that it was necessarily talking a specific subset of a statute…
Sensenbrenner’s reply? “That rates four Pinocchios”.
Were Clinton’s e-mails sent to a “foreign entity”?
Rep. Louie Gohmert (R-TX) revealed that virtually all of Hillary Clinton’s e-mails were sent to a foreign entity and the FBI didn’t bother to follow-up on the finding.

Gohmert detailed:
The Intelligence Community Inspector General (ICIG) Chuck McCullough sent his investigator Frank Rucker… to brief you [Strzok]… about an anomaly they had found with Hillary Clinton’s e-mails… When they had done the forensic analysis, they found that her emails – every single one except four – over 30,000, were going to an address that was not on the distribution list… To an unauthorized source that was a foreign entity unrelated to Russia…
To continue reading: 3 Key Takeaways From The Disastrous Strzok Hearing