Two powerful women senators, Claire McCaskill and Kirsten Gillibrand, both Democrats, took the lead on one of the most vexing problems facing the military: How to combat sexual assault and reform the system so perpetrators get punished, and victims are protected.

Each has worked aggressively for many months to win support from their colleagues, and they disagree on one key provision. Their bills will be tested next week in side-by-side votes that will allow either or both measures to proceed if they muster the 60 votes required to overcome a filibuster.

Gillibrand said she is confident she will have the necessary 60 votes. With 55 senators, including 10 Republicans, publicly supporting her legislation to move sexual-assault investigations to independent military prosecutors and away from the chain of command, Gillibrand has proved tenacious in taking on the big guns in her party. Defense Secretary Chuck Hagel and Sen. Carl Levin, the chairman of the Senate Armed Services committee, back McCaskill, who favors keeping the chain of command for these crimes, but with modifications to give victims more protection.

“We have privately more than 55 and she continues to meet one on one with colleagues on both sides of the aisle, and we believe before the gavel comes down we will have the 60 votes we need,” says Gillibrand spokesman Glen Caplin. In any event, Caplin says that Gillibrand will be voting to allow McCaskill’s bill to proceed to a vote—even as it is all but certain that McCaskill won’t return the favor, and will vote to block the Gillibrand bill. “We don’t view them as competitive bills,” he says.

McCaskill’s bill is expected to garner more than the 60 votes needed. It builds on earlier reform measures that she succeeded in getting into the defense authorization bill, and that are now law. The McCaskill bill that senators will vote on next week would strip the “good soldier defense,” which allows perpetrators to use length of service and past evidence of good military character as a legitimate defense. Gillibrand supports the measure, as she did McCaskill’s other reforms; she just doesn’t think it goes far enough.

“There is a real and honest and deep disagreement on this one policy, but Sen. Gillibrand has an enormous amount of respect for Sen. McCaskill and looks forward to voting for her bill,” says Caplin.

Both women insist they bear no personal animosity toward the other, and in an email McCaskill sent to her supporters, she attributes the “outsized attention” to her differences with Gillibrand to media preoccupation with a debate between two strong Democratic women. “I’ve wondered if this one area of disagreement… would be getting the same attention if it were a debate between men.”

The debate over how to handle sexual-assault cases is one of the rare issues in Congress that does not divide along partisan lines, left versus right. McCaskill has Republicans John McCain, Lindsey Graham, and Kelly Ayotte supporting her position. Gillibrand has Republican firebrands Ted Cruz and Rand Paul on her side, along with liberal California Sen. Barbara Boxer. Many Republicans have hung back and not made their views publicly known, and Gillibrand may find the handful of votes she needs among this silent minority, though chain-of-command tradition resonates strongly with the GOP as well.

The Senate votes will take place against the backdrop of a court-martial that got underway Tuesday in a Fort Bragg courtroom, where assertions made by Gillibrand and McCaskill will be tested in real-time. Army Brig. Gen. Jeffrey Sinclair is fighting serious allegations by his ex-lover, and advocates both for and against keeping such a prosecution within the chain of command can find reason to support their position.

McCaskill cites her background as a former prosecutor of sex crimes to underscore her belief that taking these crimes out of the chain of command would lead to fewer prosecutions and fewer protections for victims; she cites various experts to support her view. Gillibrand comes at the issue more from the perspective of those that are injured. She held the first hearing in nine years in Congress that featured a panel of victims, including the first male victim to testify.

Gillibrand’s approach takes on the system and upends it, while McCaskill works from the inside to make less radical and perhaps more achievable reforms. Who is right? Ultimately, 60 votes will decide. Lawrence Korb, a senior fellow at the Center for American Progress and a former Defense Department official, says Gillibrand is right “because commanders have a vested interest in the outcome, and you don’t need that,” he says. “Let the lawyers do it.”

If prosecution is left within the chain of command, commanders will downplay crimes because it reflects badly on them. “The reason you’re having all these sexual assaults, you’re not a good leader,” is what they fear, and that is damaging when you’re up for a promotion. “Go to a separate chain of command, just like you would go to the police or a district attorney if something happened at work,” says Korb. “You could go to your boss, but you probably wouldn’t.” It sounds simple and obvious, but not when you’re challenging the history and tradition of a great military, and you’re reshaping long entrenched attitudes.