The Senate just passed its fiscal 2016 defense authorization bill, but Armed Services Chairman John McCain and his House counterpart, Mac Thornberry, are already saying a compromise can be reached on final legislation within weeks.

Speaking to reporters last week, shortly after the Senate passed its version of the defense policy legislation, the Arizona Republican expressed confidence he and Thornberry, who helms House Armed Services, could wrap up a formal conference early in the next month.

“I am totally convinced we can get the bill back out of conference in July, and probably early July,” McCain said.

In the absence of a Senate-passed defense bill in the past two years, the chambers have not convened a formal conference committee for the NDAA, instead hammering out a final bill through informal talks between the “Big Four” chairmen and ranking members of House and Senate Armed Services committees. The June 18 vote was the first time the Senate had passed its own defense policy bill since December 2012.

Thornberry has made similarly bullish comments on how quickly the NDAA can be wrapped up. For both lawmakers, the disagreements are nuances, not substantive policy differences.

“There are not significant differences,” McCain said. “Our reforms go quite a bit further than those in the House bill, but I have a very close working relationship with the chairman of the House Armed Services Committee and I’m confident we can resolve those differences and resolve them quickly.”

Both McCain and Thornberry have a veto threat hanging over their heads, with the president promising to nix all four defense policy and appropriations bills should they land on his desk. McCain told reporters he couldn’t be sure the Senate, which passed the measure by a 71-25 vote, could override a veto given “pressures that may be exerted” on Democrats by the White House, but he’s asked Defense Secretary Ashton B. Carter for his input in conference.

“I had breakfast with the secretary of Defense this morning, and I said, ‘Look, we’re going to go to conference with the House. You tell us where you think we can find common ground on the areas that you’re in disagreement with,’” McCain said. “So I hope that we could resolve some of those differences that they have with the bill by working together.”

Thornberry Talks Tough On Veto Threat

Thornberry urged President Barack Obama to drop his veto threat, arguing that rejecting the $612 billion measure would be a reckless move.

Speaking at the Atlantic Council on U.S.-Russia policy Tuesday morning, the Texas Republican said signing defense legislation (HR 1735) could go a long way in reassuring NATO allies, with whom Carter is meeting in Europe this week.

“My suggestion is nothing would send a stronger signal … than for the president to agree to sign the defense bills with the money that he asked for,” Thornberry said.

The White House has threatened to veto all policy and appropriations legislation that “locks in” sequestration spending levels and it has pushed for a repeal of both defense and non-defense discretionary spending caps, while Republicans have contended the global threat situation requires increased defense spending and quick action on defense policy legislation. Thornberry chalked up the White House’s threat to veto the legislation, which does not allocate any funds, to “political hysterics … or to provoke a confrontation” with Congress over the budget.

“The defense authorization bill is basically the policy bill,” he said. “So to threaten to veto that really makes no sense.”

If Obama is set on vetoing the legislation, he could receive the bill sooner rather than later. Thornberry said he and McCain would likely begin meeting this week to start working out the differences in their bills, though he downplayed areas of contention between the two measures.

“There’s not a lot of differences. They’re largely along the same track,” he said.

Thornberry gave no indication the veto threat would sway him or a potential conference committee to produce a bill the president would be more likely to sign.

“What we’re going to try to do over the next month is to work out the House-Senate differences, get that final conference report, pass it out of the House and Senate and give him the opportunity,” Thornberry said. “I hope he will do the right thing.”

Senate Armed Services ranking member Jack Reed said he believes informal staff-level discussions will begin this week to resolve differences in the two versions of the authorization measure. But in-depth discussions between the leaders of the two committees will likely wait until after the July 4 recess.

In the Senate, members are “just getting into the details” of the House bill, after being focused on getting their own legislation through the chamber, the Rhode Island Democrat said.

Differing on Acquisition Reform

Perhaps the biggest issue for the two chairmen to reconcile will be their proposals to revamp the way the Pentagon buys its weapons. Both McCain and Thornberry have made acquisition overhaul a top priority, a point McCain reiterated last week, but it is unclear how the two Republicans might come together.

“We’re both in agreement that reform is badly needed when you look at these outrageous and disgraceful cost overruns,” McCain said.

Other differences between the two bills include provisions related to detainees at the Guantánamo Bay, Cuba, detention facility. While both measures would put new limits on the Pentagon’s authority to move the detainees, the House bill contains more restrictive language, which lasts two years from enactment. The Senate bill, on the other hand, would permit detainees to be transferred to the United States for medical treatment and would permit the administration to shut down the prison after Congress approves a plan from the president on how it would deal with the remaining detainees.

The Senate bill also includes language, added as an amendment during the Armed Services markup, that would permit the transfer of additional Overseas Contingency Operations funds to the base Pentagon budget in the event of a new budget deal that raises defense and non-defense spending caps by proportionally equal amounts.

Megan Scully contributed to this report.