Sen. Claire McCaskill, D-Mo., a vocal advocate against sexual violence in the military, is under fire from former allies who now claim that McCaskill's reform proposal could let sexual predators "go free."

McCaskill was caught off guard last week when Terri Odom, a sexual assault survivor who says she "absolutely adores" McCaskill, joined an effort to pressure the senator to reverse her proposal to curb military sexual assaults just as it was advancing through the Senate.

At the heart of the dispute is McCaskill's proposal to allow military commanders to continue deciding whether sexual-assault cases are prosecuted, rather than leave that decision to outside lawyers, as her opponents propose.

It's no small difference, charge her one-time allies.

"Without your support, perpetrators may continue to go free; victims will be too afraid to come forward; and our military readiness will suffer," Odom wrote in an open letter to McCaskill published in the St. Louis Post-Dispatch.

Protect Our Defenders, a victims' advocacy group on whose advisory board Odom sits, has also run ads against McCaskill both online and in a local Missouri newspaper, despite a record of working with the senator.

The perceived friendly fire from one-time allies has frustrated McCaskill, who has built a reputation for being an aggressive advocate on the issue.

McCaskill supports an initiative that would keep the military chain of command involved in the prosecution of sexual assault cases, while adding new checks. Sen. Kirsten Gillibrand, D-N.Y., is leading the charge backed by McCaskill's critics for an alternative reform that would have independent prosecutors tasked with deciding which sexual-assault cases are prosecuted.

Protect Our Defenders says McCaskill brought the criticism on herself with three recent public statements.

"We decided to publish this open letter from Terri Odom when we did because of Sen. McCaskill's recent remarks on the issue that have rightfully upset many victims," said Brian Purchia, the group's spokesman. "She owes them an explanation."

The remarks that so upset her former allies include the suggestion that McCaskill would support Gillibrand's proposal only if there's a drop in the number of victims coming forward or if fewer sexual-assault predators are convicted "five years from now."

In the same interview, with The Nation, McCaskill defended her proposal, arguing that having a commander decide to prosecute a sexual assault sends a message to others in the unit and “gives [the victim] a level of protection you will never have when everyone knows a bunch of outside lawyers have bought your bull.”

“Bull? She is not only attacking the competence and credibility of military prosecutors, her words seems to imply that a large percentage of the victims who report are lying,” Purchia told the Washington Examiner in an email.

McCaskill’s office’s appeared bewildered by the accusations, calling the group’s criticisms “unfortunate.”

“Claire McCaskill has been accused of many things, but this is the first time she’s ever been attacked by someone claiming that she’s not completely committed to protecting victims of sexual assault and putting predators behind bars,” said McCaskill spokeswoman Anamarie Rebori. “It’s unfortunate that a group sharing her goals has taken the debate in this direction.”

Odom, a Missouri resident and the author of the Post-Dispatch letter, told the Examiner she “absolutely adores” McCaskill, but was “shocked” by the senator’s proposal.

“That letter was incredibly hard for me,” said Odom, who described having had rocks thrown at her while going door-to-door using a walker to canvass for McCaskill’s campaign. “I happen to adore and worship Sen. McCaskill. She is the strongest senator in the Senate. She will always have my vote.” 

Odom said she expects to meet with McCaskill in August to discuss her concerns.

Being under fire for being insufficiently aggressive on military sexual assault is an odd position for McCaskill.

She recently put a hold on a promotion for Air Force Lt. Gen. Susan Helms after Helms overturned a 2012 sexual assault conviction. While questioning the highest-ranking military officer in the nation – Chairman of the Joint Chiefs of Staff Gen. Martin Dempsey – an agitated McCaskill said she would be “in front of the line to kick you until you’re senseless” if the problem was not addressed soon.

And Protect Our Defenders has previously praised McCaskill for her “leadership” on the issue.

But the group says that, while they appreciate McCaskill’s previous work on the issue, their interests align with Gillibrand’s for the time being.

"Sen. McCaskill's proposal really does nothing new. It really defers to the military for self-policing and self-regulation. … That's simply not enough,” said the group's executive director, Taryn Meeks. “The military has proven that it's not up to the task, that fundamental change must be made from the outside.”