WASHINGTON » A U.S. senator remains steadfast in blocking the nomination of Air Force Lt. Gen. Susan Helms, tapped to serve as vice commander of the U.S. Space Command, over serious concerns with Helms’ decision to overturn a jury conviction in a sexual assault case.

Sen. Claire McCaskill, D-Mo., who first put a hold on the nomination in April, said she met with Helms and Air Force officials yet still had reservations.

"At a time when the military is facing a crisis of sexual assault, making a decision that sends a message which dissuades reporting of sexual assaults, supplants the finding of a jury, contradicts the advice of counsel and further victimizes a survivor of sexual assault is unacceptable," said McCaskill, a member of the Senate Armed Services Committee.

McCaskill’s hold effectively prevents the Senate from approving Helms’ nomination.

In February 2012, Helms rejected the recommendation of legal counsel and overturned the conviction of an Air Force captain who had been found guilty of aggravated sexual assault of a female lieutenant.

McCaskill explained her objections in a statement in the Congressional Record on Thursday.

"Lt. Gen. Helms has a record of more than thirty years of distinguished military service, in which she became the first American military woman in space, among other significant achievements. Her career is to be celebrated," McCaskill said. "However, I continue to have deep concerns with Lt. Gen. Helms’ decision, while a commander and courts-martial convening authority, to overturn the jury verdict of a military court martial in which the jury found an Air Force officer guilty of sexual assault. She made this decision against the advice of her staff judge advocate."

The Helms’ situation echoes another Air Force case that has outraged members of Congress and prompted them to move swiftly on legislation that would strip commanders of the authority to overturn convictions.

Lt. Gen. Craig Franklin, commander of the 3rd Air Force at Ramstein Air Base in Germany, overturned a conviction against Lt. Col. James Wilkerson, a former inspector general at Aviano Air Base in Italy. Wilkerson had been found guilty last Nov. 2 of charges of abusive sexual contact, aggravated sexual assault and three instances of conduct unbecoming of an officer and a gentleman. The incident had involved a civilian employee.

Wilkerson was sentenced to a year in prison and dismissal from the service. But after a review of the case Franklin overturned the conviction.