The tarmac meeting was not a good idea.

In the final days of the Clinton investigation, the attorney general at the time, Loretta E. Lynch, held an impromptu private meeting with former President Bill Clinton when the two found themselves unexpectedly on the same tarmac at Phoenix Sky Harbor International Airport. The meeting led to calls for Ms. Lynch to recuse herself from the investigation. She did not, but said she would defer to the F.B.I. and career prosecutors on whether to prosecute Mrs. Clinton. The tarmac meeting, as well as Ms. Lynch’s half-in-half-out response, are expected to be criticized in Thursday’s report. Ms. Lynch has already said she regrets the meeting.

What about those text messages?

Two F.B.I. officials, who were assigned to both cases, exchanged text messages that revealed strong anti-Trump sentiment. They said Mrs. Clinton “just has to win” and described a potential victory by Mr. Trump as “terrifying.”

Mr. Trump’s supporters have seized on these messages as evidence that the F.B.I. was biased against him. The inspector general is expected to criticize the officials, Peter Strzok and Lisa Page, but his conclusions on the matter will be closely watched. F.B.I. regulations allow agents to express opinions both “privately and publicly on political subjects and candidates.”

Will Giuliani make an appearance?

Mr. Horowitz has said he is investigating whether officials improperly disclosed information about the Clinton case to journalists. But one of the most intriguing questions involves the potential leak of information to one of Mr. Trump’s key campaign surrogates, Rudolph W. Giuliani. Mr. Giuliani appeared on Fox News in October 2016 and hinted that big news was about to break:

“I mean, I’m talking about some pretty big surprises,” he said in one interview. In another, he referenced Mrs. Clinton and said he expected the surprises to surface in the coming days.

Two days later, Mr. Comey broke the news that the F.B.I. was once again investigating Mrs. Clinton and her emails. Mr. Comey has said he ordered an investigation into that disclosure but it is not clear what came of it.

Mr. Giuliani is now a lawyer for Mr. Trump, who has railed against inappropriate disclosures to reporters.

Was the F.B.I. slow to respond?

The inspector general is expected to criticize officials at F.B.I. headquarters for the speed at which they responded to the discovery of new emails on a laptop belonging to the estranged husband of one of Mrs. Clinton’s top aides. Critics, including some inside the F.B.I., have suggested that officials at headquarters were uninterested in revisiting the investigation before the election.