Given that there have been about 30 treason trials in the United States since 1789, bringing treason charges against Snowden would be problematic, but not unheard of.

The whole concept of treason is an important part of the Constitution. The Founding Fathers knew the British laws about treason all too well. The British laws were much broader than our current definitions, and treasonable offenses include having sexual relations with the king's wife, counterfeiting, and the murder of a husband by a wife.

In fact, the men who signed the Declaration of Independence knew they risked treason charges if things didn't work out well.

Article 3, Section 3 of the Constitution spells out what is considered treason in the United States:

"Treason against the United States, shall consist only in levying War against them, or in adhering to their Enemies, giving them Aid and Comfort. No Person shall be convicted of Treason unless on the Testimony of two Witnesses to the same overt Act, or on Confession in open Court. The Congress shall have Power to declare the Punishment of Treason, but no Attainder of Treason shall work Corruption of Blood, or Forfeiture except during the Life of the Person attainted."

Among the treason trials in the past two centuries were the acquittal of Aaron Burr, the former vice president, and the convictions of abolitionist John Brown, the four Abraham Lincoln assassination conspirators, and alleged spy couple Ethel and Julius Rosenberg.

The U.S. legal code spells out the punishments for treason, which includes death.

"Whoever, owing allegiance to the United States, levies war against them or adheres to their enemies, giving them aid and comfort within the United States or elsewhere, is guilty of treason and shall suffer death, or shall be imprisoned not less than five years and fined under this title but not less than $10,000; and shall be incapable of holding any office under the United States."

The Rosenbergs were the last people in the U.S. involved in a treason trial to be convicted, sentenced to death, and then executed. Their execution in 1953 was debated globally and was seen as an important development in the Cold War and the expansion of the era of McCarthyism.

Today, several senators, including Dianne Feinstein, want Edward Snowden taken into custody, returned to the United States, and put on trial for treason, which Congress has a right to advocate for under the Constitution.

"I don't look at this as being a whistleblower. I think it's an act of treason," Feinstein, the chairwoman of the Senate Intelligence Committee told reporters. "He violated the oath, he violated the law. It's treason."

Former U.S. Ambassador John Bolton told a Chicago radio show that Snowden should face treason charges.

"He took an oath to keep the secrets that were shared with him so he could do his job. He said he would not disclose them, and he lied," Bolton said.

Speaker of the House John Boehner also called Snowden "a traitor" in a Tuesday interview with ABC. "The disclosure of this information puts Americans at risk, it shows our adversaries what our capabilities are, and it's a giant violation of the law."

One of the most recent American citizens charged with treason is Adam Yahiye Gadahn, the California-born spokesman for al-Qaida. In 2006, Gadahn was indicted in the Central District of California for treason and giving material support to al-Qaida. He remains in hiding overseas.

Anwar Al-Awlaki, the U.S.-born al-Qaida member, was never formally charged with treason. Instead, he was killed in a drone attack in 2011 in Yemen.

John Walker Lindh, an American citizen who was captured fighting for the Taliban, wasn't charged with treason when he accepted a plea bargain in court. He was indicted on 10 other charges by a federal grand jury.

Bradley Manning, the Army private who gave various documents to the WikiLeaks website, is currently facing court-martial. Manning has already agreed to plead guilty to 10 lesser criminal charges, but he faces violations of the Espionage Act and charges of aiding the enemy under military law (which carries a potential death penalty).

There were multiple reports on Tuesday that the Justice Department was preparing charges against Snowden, which would need to be filed so that it can make an extradition request. There was no information about the exact charges he would face.

Snowden is currently believed to be in Hong Kong.

One problem for the government, if and when Snowden is in custody, is the task of proving Snowden gave aid and comfort to the enemy, one of the requirements of a treason charge under the Constitution.

Former judge Andrew P. Napolitano told Fox News that the federal government will have to make the case that Snowden knowingly tried to aid an enemy of the United States by disclosing this information.

He believes the Justice Department will pursue charges of violating a security clearance, but it could "overcharge" Snowden with spying charges as a bargaining position.

Mark Zaid, a national security lawyer who represents whistleblowers, told the Associated Press that Snowden could face decades in prison if he is successfully returned to the United States.

Zaid said the government could subject Snowden to a 10- or 20-year penalty for each document he leaked.

Another challenge for the Justice Department and the Obama administration would be the publicity that would accompany treason charges for Snowden.

Scott Bomboy is the editor-in-chief of the National Constitution Center.