After a year of focused debate, advocates for changing a culture of rampant sexual assault within the military were rebuked by a 55-45 procedural vote in the Senate Thursday that did not allow the measure to advance to a full vote.

The Military Justice Improvement Act (S. 1752), sponsored by Sen. Kristen Gillibrand (D-NY), would remove the chain of command from the adjudication process for military sexual assault. Supporters of the blocked measure said the bill would make it more likely that victims would report crimes and see justice.

Upon its failure to proceed to a general vote on Gillibrand’s proposal, the Senate voted to advance the Victims Protection Act (S. 1917), sponsored by Sen. Claire McCaskill (D-MO), which would retain the authority of the commanders to deal with sexual assault within their ranks and introduce other, more moderate, reforms designed to lessen the occurrence of sexual assault within the military.

The floor debate Thursday was polite yet passionate, and focused more on support or opposition to Gillibrand’s proposal rather than the merits of one approach over the other. McCaskill’s supporters spent most of their floor time describing why they opposed the Military Justice Improvement Act rather than why they supported the reforms proposed in the Victims Protection Act. Speaking to her measure shortly before the vote, Gillibrand implored the chamber to “listen to the victims” and characterized arguments on the floor against her measure as technical in focus.

As covered extensively by Adele Stan for Rewire, Gillibrand has tenaciously pursued her measure. The senator went into the floor debate with 55 known supporters of her bill, including not just reliable advocates for improving conditions for women in the military, such as Sen. Barbara Boxer (D-CA) and Sen. Jeanne Shaheen (D-NH), but also more conservative members, including Sens. Chuck Grassley (R-IA), Rand Paul (R-KY), and David Vitter (R-LA).

Speaking on the floor against Gillibrand’s measure, Sen. McCaskill said, “We cannot let the commanders walk away.” She was joined by Sen. Lindsey Graham (R-SC), who spoke to the matter of sexual assault in the military with a view likely not shared by the scores of those victimized. “The worst thing that could happen in a unit is for the commander to say that this is no longer my problem,” he said. Also opposing the Gillibrand measure and supporting the McCaskill proposal was Sen. James Inhofe (R-OK), who serves as ranking member on the Armed Services Committee.

The Pentagon estimated in a report for the 2012 fiscal year that there were 26,000 incidents of sexual assault within the military, with fewer than 3,400 of them reported.

Having failed to proceed to a general vote, the Military Justice Improvement Act has been returned to the full Senate calendar.