The Senate began floor debate Thursday on the Trump administration’s $67.4 billion Iran war supplemental, opening one of the most consequential weeks of war-related legislating in a generation as a separate bipartisan war powers resolution accumulated cosponsors at a pace that aides in both caucuses said had caught leadership off guard.

The first procedural vote, a motion to proceed offered shortly after 10 a.m. by Senate Appropriations Chair Susan Collins, R-Maine, carried 71-27, well above the 60-vote threshold and with the support of a clear majority of both caucuses. The wide margin reflected what Collins called “a recognition that troops in the field need certainty,” but it concealed sharper disagreements over the conditions attached in committee — and over whether the chamber, having funded the war, would also vote to define it.

“This is the moment the Senate asserts itself,” Collins said in floor remarks opening the debate. “We are providing the resources, and we are providing the framework. The two are inseparable.”

The supplemental as reported out of committee Monday includes a 90-day operational reporting requirement, a Sept. 30 cutoff on combat operations absent reauthorization, and a near-doubling of the casualty assistance line to $12.1 billion. A package of nine amendments was made in order Thursday morning under a unanimous consent agreement negotiated overnight by Senate Majority Leader Chuck Schumer, D-N.Y., and Minority Leader John Thune, R-S.D. Among them: a strike-and-replace proposal from Sen. Tom Cotton, R-Ark., that would remove the Sept. 30 cutoff; a tightening amendment from Sen. Chris Murphy, D-Conn., that would shorten the reporting cycle from 90 to 45 days; and a bipartisan provision from Sens. Mark Kelly, D-Ariz., and Joni Ernst, R-Iowa, that would create a standing Senate-House oversight panel modeled on the Iraq Study Group’s later iterations.

Schumer told reporters before gaveling in that he expected final passage of the supplemental “by Friday evening, possibly Saturday,” and that the parallel war powers resolution introduced by Sens. Tim Kaine, D-Va., Mike Lee, R-Utah, and Murphy was now “on track for a floor vote no later than Friday.” The resolution carried 38 cosponsors as of Thursday morning, an increase of seven in 48 hours, with two additional Republicans signing on overnight after a closed-door members-only briefing Wednesday evening from senior defense and intelligence officials.

“Members are not where they were two weeks ago,” Kaine said in a brief hallway exchange. “They have heard the casualty numbers. They have heard what the operational tempo looks like into the summer. They are not voting to end the war today. They are voting to make sure that whatever comes next has a vote behind it.”

The Pentagon updated its casualty figures again Thursday morning. Defense Department spokeswoman Sabrina Singh told reporters that three additional U.S. service members had died of wounds sustained in earlier strikes, bringing the cumulative total since the war’s onset to 358. More than 1,240 have been wounded. “Each of these losses is a permanent fact for a family in this country,” Singh said. “The department’s obligation does not end when the headlines move on.”

White House posture, which had hardened earlier in the week, appeared to soften as the day progressed. President Donald Trump, asked by a reporter on the South Lawn whether he would sign the supplemental in its current form, said he had been “talking to the senators, and we’re going to work it out — we always work it out.” Press Secretary Karoline Renfro, in the afternoon briefing, said the administration “shares the goals of accountability that the committee has articulated” but continued to oppose what she called “an arbitrary calendar deadline on the men and women in uniform.”

Vice President JD Vance spent much of Thursday on Capitol Hill, moving between Senate offices through a back corridor to avoid press cameras. A senior administration official, granted anonymity to describe internal deliberations, said Vance had been authorized to negotiate on the reporting requirement and the casualty-assistance topline but had been instructed to draw a line at the Sept. 30 cutoff. “That number is not a number we can live with,” the official said. “Everything else is conversation.”

Republican leadership remained publicly opposed to the war powers resolution but visibly less unified than even a week earlier. Thune, asked outside the chamber whether he intended to whip against the Kaine-Lee-Murphy measure, said only that he had “shared my views with my members and I will let them vote their conscience.” Two GOP leadership aides, speaking on condition of anonymity, said the working assumption inside the conference was that the resolution would pass with between 54 and 58 votes — a margin that would not survive an expected presidential veto, but that would establish a marker many senators saw as overdue.

On the Democratic side, the dynamic was nearly inverted. Senate Foreign Relations Chair Bob Menendez of New Jersey, who had moved carefully in the early weeks of the war, told reporters Thursday that he would vote for the resolution. So did Sen. Mark Warner, D-Va., who described his thinking in similar terms to comments he had offered Monday. “We owe the country a vote,” Warner said. “We owe ourselves a vote. We owe the troops a vote.”

The Islamabad track, where Pakistani, Saudi and Egyptian mediators have been pushing a set of framework principles between Iranian and U.S.-Israeli interlocutors, hovered over the floor debate. Several senators in both parties suggested that a credible diplomatic opening could relieve some of the pressure for a binding war powers vote — but only if it materialized within days. “We are not legislating in a vacuum,” said Sen. Chris Coons, D-Del., chair of the Senate Foreign Relations subcommittee on the Middle East. “If there is a diplomatic path that produces a halt, that changes the calculus on the floor. If there is not, this vote happens, and it happens this week.”

Reema Khoury, a former Senate Foreign Relations Committee aide now at the Stimson Center, said the convergence of the supplemental, the war powers resolution and the Islamabad talks had produced a moment “without recent precedent” in congressional war oversight. “The institutional pieces are moving at roughly the same speed for the first time,” Khoury said. “Whether they arrive at the same place — that is what Friday will tell us.”

Floor action was set to resume Friday morning at 9 a.m. Schumer said he expected the chamber to remain in session through the weekend if necessary.