FBI Director James Comey is set to appear before the House Oversight Committee Thursday amid a fierce backlash over his decision earlier this week to recommend that the Justice Department decline to pursue criminal charges against Hillary Clinton for her "extremely careless" handling of classified information.

The decision rankled Republicans and prompted four congressional leaders to pursue hearings or probes that could shed additional light on the FBI's decision.

Rep. Jason Chaffetz, chairman of the Oversight Committee, said he found Comey's announcement " surprising and confusing" given the gap between the case against Clinton he laid out and the conclusion he drew from it.

The move to end the Clinton email probe without charging anyone involved with a crime has raised many questions among skeptical observers. Here are seven that Comey could face at the oversight hearing Thursday.

1. What about the Clinton Foundation?

The FBI's investigation had reportedly expanded to include the activities of the Clinton Foundation months before Comey concluded its work.

Anonymously-sourced reports had indicated FBI investigators were looking into allegations of "public corruption" stemming from the intersection of the foundation and the State Department under Clinton.

Matthew Whitaker, president of the Foundation for Accountability and Civic Trust, said the public corruption probe is likely still underway.

"I am presuming that, based on reports, that that investigation continues and is still outstanding," Whitaker said, acknowledging that it would be difficult to know for certain.

The Clinton Foundation has come under fire for accepting large foreign donations while Clinton served as secretary of state, creating potential conflicts of interest when foundation donors seemingly received preferential treatment from Clinton's State Department.

David Bossie, president of Citizens United, said that Comey's announcement Tuesday has no bearing on the question of the Clinton Foundation investigation.

"I think that the pressure on the FBI to make a statement on the email case was gaining on the FBI, that they needed to make a decision," Bossie said.

"I think that they got started later on the public corruption case, and so I wouldn't necessarily expect an announcement on that anytime soon," he added.

2. Why did Bryan Pagliano need an immunity agreement if no laws were broken?

Clinton's information technology specialist struck an immunity deal with the Justice Department in exchange for his testimony about how the server system was set up.

Pagliano invoked his Fifth Amendment rights and refused to answer questions about the email controversy when called before the House Select Committee on Benghazi last year and when pulled into a deposition in a Freedom of Information Act lawsuit.

His lawyers cited reasonable fear of self-incrimination when attempting to avoid the deposition last month.

3. What reason did witnesses give for setting up the servers in the first place?

Clinton has repeatedly argued since March of last year that she set up her private email system for "convenience," in order to consolidate her work and personal accounts on one mobile device.

That reasoning has been debunked consistently by reports that Clinton carried multiple devices and was impeached entirely by Comey when he announced that, not only did Clinton carry several different devices, but she hosted her emails on multiple servers.

Critics have contended that Clinton set up the network to shield her communications from open-records requests in anticipation of her presidential campaign.

Whatever the true motivation for setting up the private servers, evidence does not support Clinton's claim that it was a matter of convenience.

4. How much did this investigation cost?

Sen. Ron Johnson, chairman of the Senate Homeland Security Committee, has already asked the Justice Department to provide an estimate of the cost to taxpayers of the Clinton email investigation.

Comey said the process of piecing together deleted records from Clinton's multiple servers was "painstaking" and consumed significant agency resources.

Congressional Republicans in particular may be interested in the figure because Democrats have repeatedly used the roughly $7 million price tag of the House Select Committee on Benghazi's probe as a political weapon. GOP lawmakers could attack Clinton for misconduct that forced a large expenditure of taxpayer money if the cost of the FBI's investigation turns out to be steep.

5. Why was a special prosecutor never appointed?

Republicans have been calling on Attorney General Loretta Lynch to appoint a special prosecutor to rule on the Clinton email case since September of last year amid fears that political bias could affect the Justice Department's ultimate decision.

Although Lynch repeatedly argued such an appointment was not necessary due to her agency's commitment to impartiality, her judgement was called into question last week after a reporter exposed her secret meeting with Clinton's husband aboard a private jet.

A special prosecutor could have eliminated some of the backlash over potential bias in the Clinton email probe by cutting political appointees out of the decision-making process.

6. How is "extreme carelessness" different from "gross negligence"?

GOP lawmakers have demanded Comey explain how the " extreme carelessness" in handling classified information that he attributed to Clinton and her aides differs from the "gross negligence" that constitutes a violation of the law.

Rudy Giuliani, former mayor of New York City and a former U.S. attorney, suggested during an appearance on MSNBC Wednesday that there was virtually no daylight between the two characterizations in the eyes of the law.

Much of the outrage surrounding Comey's decision has centered on the fact that the evidence against Clinton made public Tuesday amounted to a compelling case that the former secretary of state had broken laws, but was not strong enough to convince Comey to recommend a criminal indictment.

7. Were the FBI recommendations to Lynch the same for every individual involved in the Clinton email network?

Whitaker said Comey's remarks Tuesday left the door open for aides involved in the Clinton email controversy to face criminal charges, even if Clinton herself had been cleared.

"I'm probably reading the tea leaves a little bit, but I do think the door is still open for some of the other people involved to potentially still face consequences because they all had different roles," he said.

During an appearance on Fox News Tuesday, Chaffetz said he had asked Comey whether individuals other than Clinton could be charged for their involvement in transmitting classified material. He said he asked specifically about the fate of Bryan Pagliano, the technology aide who received an immunity agreement in exchange for his testimony about how the private server system was set up.

Chaffetz said Comey responded that he was unable to comment.

But Lynch's announcement late Wednesday that no one involved in the investigation would be charged shut the door on indictments for the aides who forwarded Clinton some of the most sensitive emails related to the probe.

Comey could face questions about whether he recommended indictments for others, such as Cheryl Mills, Huma Abedin or Jake Sullivan.