House and Senate negotiators officially kicked off talks Thursday to reconcile their versions of the annual defense policy bill with several thorny debates looming over them.

Chief among them is how to deal with Pentagon funding that has been tapped for President Trump Donald John TrumpFederal prosecutor speaks out, says Barr 'has brought shame' on Justice Dept. Former Pence aide: White House staffers discussed Trump refusing to leave office Progressive group buys domain name of Trump's No. 1 Supreme Court pick MORE’s border wall.

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Negotiators will also wrangle with an amendment meant to block Trump from taking military action against Iran, a provision that has received renewed attention as Trump debates how to respond to attacks on Saudi oil facilities.

Ahead of the first official meeting — dubbed the “pass the gavel” meeting — the leaders of the Armed Services committees would not indicate where they will land on those and other issues.

“I appreciate the questions, but we’re not going to tell you how we’re going to have an outcome here at this press conference, in part because we don’t know what that outcome is yet,” House Armed Services Committee Chairman Adam Smith David (Adam) Adam SmithOvernight Defense: Appeals court revives House lawsuit against military funding for border wall | Dems push for limits on transferring military gear to police | Lawmakers ask for IG probe into Pentagon's use of COVID-19 funds Democrats push to limit transfer of military-grade gear to police 40 groups call on House panel to investigate Pentagon's use of coronavirus funds MORE (D-Wash.) told reporters. “That’s the nature of a conference committee.”

Smith was speaking to reporters alongside Senate Armed Services Committee Chairman James Inhofe James (Jim) Mountain InhofeOvernight Defense: Appeals court revives House lawsuit against military funding for border wall | Dems push for limits on transferring military gear to police | Lawmakers ask for IG probe into Pentagon's use of COVID-19 funds Democrats push to limit transfer of military-grade gear to police Chamber of Commerce endorses McSally for reelection MORE (R-Okla.), Senate Armed Services ranking member Jack Reed John (Jack) Francis ReedOvernight Defense: Appeals court revives House lawsuit against military funding for border wall | Dems push for limits on transferring military gear to police | Lawmakers ask for IG probe into Pentagon's use of COVID-19 funds Democrats push to limit transfer of military-grade gear to police When 'Buy American' and common sense collide MORE (D-R.I.) and House Armed Services Committee ranking member Mac Thornberry William (Mac) McClellan ThornberryOvernight Defense: Appeals court revives House lawsuit against military funding for border wall | Dems push for limits on transferring military gear to police | Lawmakers ask for IG probe into Pentagon's use of COVID-19 funds Democrats push to limit transfer of military-grade gear to police Trump payroll-tax deferral for federal workers sparks backlash MORE (R-Texas).

Though Thursday marked the first formal meeting of the conference committee, staffers and key lawmakers have been talking behind the scenes for months.

Earlier this month, the Pentagon announced it was taking $3.6 billion from 127 military construction projects to build 175 miles of wall on the U.S.-Mexico border, in line with Trump’s emergency declaration at the beginning of the year.

The Senate’s version of the National Defense Authorization Act (NDAA) would replace that $3.6 billion, while the House’s would not.

A school of thought has emerged ahead of the NDAA negotiations that the issue is an appropriations issue not an authorization one since the projects losing money to the wall are authorized for five years regardless.

As such, questions have emerged over whether negotiators will decide to be silent on the issue altogether, kicking the fight exclusively to the government funding bill.

Smith said Thursday no decision has been made on how to handle backfilling the military construction funds.

Despite the controversial issues facing negotiators, the committee leaders expressed hope they could continue the 58-year streak of getting the NDAA signed into law.

“All four of us are determined to do everything we possibly can to make it 59,” Thornberry said. “This is not just policy differences and so forth. There are flesh and blood men and women serving our country right now all over the world who are affected by the decisions we make, as well as adversaries and allies that are watching what we do.”

In addition to the border wall and Iran, lawmakers will need to find compromises on issues ranging from U.S. military support to the Saudi Arabia-led coalition in Yemen to Trump’s transgender military ban to Pentagon funds being used at Trump-owned properties.