What happens if you lie to Congress

The Capitol Building.
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During FBI Director James Comey's nearly five hours of testimony before Congress on Thursday, Republicans repeatedly brought up an allegation that Hillary Clinton lied under oath during a committee hearing.

House Oversight and Government Reform Committee Chairman Jason Chaffetz went so far as to tell Comey he would request the agency investigate whether Hillary Clinton lied under oath to Congress "in the next few hours."

Later in the hearing, when pressed, Comey said the reason an investigation had not been opened yet was that, "out of respect for the legislative branch being a separate branch, we do not commence investigations that focus on activities before Congress without Congress asking us to get involved."

With that request now seeming all but guaranteed, CNBC broke down the consequences of lying to Congress in five questions.

Q: What are the rules about lying to Congress?

A: Glad you asked. If you are testifying in front of Congress sometime soon, and are wondering how far you can bend the truth, there are a two key statutes governing perjury you need to be aware of: U.S. Code sections 1621 and 1001 of Title 18.

Section 1621 covers general perjury, and stipulates that anyone who "willfully and contrary to such oath states or subscribes any material matter which he does not believe to be true" is guilty of perjury and shall be fined or imprisoned up to five years, or both. Section 1001 covers false statements more generally, without requiring an oath. The section stipulates that "whoever, in any matter within the jurisdiction of the executive, legislative, or judicial branch of the government of the United States, knowingly and willfully" falsifies or conceals information, including before a congressional committee's inquiry, may also be fined or imprisoned up to five years.

Q: What potential punishment would someone who lied to Congress face?

A: If you paid attention during the last section, you may have read that general perjury comes with a maximum five-year prison sentence and potential fine. The same basically goes for not telling the truth to Congress, even without an oath. However, if the lie under Section 1001 involves terrorism, the maximum prison sentence rises to eight years.

Seth B. Waxman, a former federal prosecutor, wrote that a punishment was unlikely.

"Certainly, the FBI could open an investigation for perjury charges, but such a case would likely be even more difficult to prove than the disclosure of classified information because there would be an even greater need to get inside the head of Mrs. Clinton; something the FBI was unable to do in the context of the disclosure of classified information."

Q: Who has ever lied to Congress?

A: This might be a tough one to answer comprehensively especially because it is extremely rare to see charges brought. In fact, a study from 2007 found just six successful convictions of perjury or related charges in relation to Congress in the previous 60 years.

However, one recent case jumps to mind, the testimony of former CIA Director Michael Hayden in which he seemingly misled Congress about the agency's interrogation program. And while it wasn't Congress, who could forget the charges that Bill Clinton in 1998 provided false testimony under oath in the Paula Jones case?

Q: Why exactly are Republicans saying Hillary Clinton lied to Congress?

A: During a 2015 hearing on the Benghazi attack, Clinton told Congressman Jim Jordan that, "[t]here was nothing marked classified on my emails, either sent or received." Comey refuted that statement Thursday, testifying that some emails on Clinton's server contained markings that indicated confidential material, although he allowed perhaps Clinton did not understand what the marking meant.

"I think it's possible — possible — that she didn't understand what a C meant when she saw it in the body of an email like that," Comey said of Clinton.

Q: What kind of political fallout will Clinton face?

A: File this away in the category of questions the Clinton campaign hopes never to answer. Republicans will use Comey's testimony to continue their efforts to paint Clinton as reckless and careless with national security, and his words will almost certainly continually play on attack ads throughout the rest of the cycle. If the past week saw Trump endure damage over a tweet many have condemned as anti-semitic, Clinton's political stock has definitely taken a hit over the past few days.

But, the ultimate impact is still to be determined.

—CNBC's Lori Ann LaRocco contributed to this report.