The former deputy commander of the storied 82nd Airborne Division was originally brought up on sexual assault charges punishable by life in prison. He was believed to be the highest-ranking U.S. military officer ever court-martialed on such charges.
But earlier this week, prosecutors dropped those charges in a deal in which Sinclair pleaded guilty to adultery with one woman and conducting inappropriate relationships with two others by asking them for nude pictures and exchanging sexually explicit email. Adultery is a crime in the military.
The case unfolded with the Pentagon under heavy pressure to confront what it has called an epidemic of rape and other sexual misconduct in the military.
Rep. Jackie Speier, D-Calif., called the sentence "laughable."
"Even when the world is watching, the military has demonstrated their incompetence at meting out justice," Speier said in a statement. "This is another sordid example of how truly broken the military justice system is. This sentence is a mockery of military justice, a slap on the wrist nowhere close to being proportional to Sinclair's offenses."
While the charges against Sinclair carried a maximum of more than 20 years in prison, the plea bargain worked out by the defense and military prosecutors called for no more than 18 months.
The judge, Col. James Pohl, did not explain how he arrived at the much lighter sentence.
Prosecutors had no immediate comment.
Under the sexual assault charges, Sinclair was accused of twice forcing a female captain to perform oral sex and threatening to kill her if she told anyone about their three-year affair in Iraq and Afghanistan.
But the case started to crumble as questions arose about her credibility and whether military officials improperly pressed ahead with a trial because of political considerations — namely, a desire to show the Army's resolve to combat sexual misconduct.
Retired Rear Adm. Jamie Barnett, a Washington lawyer who helped represent the female captain, said the woman was disappointed with the sentence. Barnett called it a "slap on the wrist."
"A sentence doesn't take away any of the pain and anguish that she has endured," Barnett said.
The Associated Press generally does not identify those who say they were sexually assaulted.
Experts in military law agreed the sentence was lenient.
"I can't believe it," said retired Lt. Col. Gary D. Solis, a former military judge who now teaches law at West Point and Georgetown University. Solis said Sinclair "is an individual who should not be a general officer. He should have gone to jail and dismissed from the Army."