Sen. John McCain (R-Ariz.) last week on Capitol Hill. (J. Scott Applewhite/AP)

Senate Armed Services Committee Chairman John McCain promised to let senators offer any amendments they want to the defense bill, paving the way for votes on several issues that will directly challenge President Trump’s national security policy.

But the promise of votes is far from a guarantee that the senators’ effort to force a reckoning on the war in Afghanistan, sanctions against North Korea, the ban on transgender troops serving in the military and other controversial policies will be successful.

A bid by Sen. Rand Paul (R-Ky.) to force Congress to decide within six months on a new authorization for use of military force (AUMF) against extremist groups failed in the chamber Wednesday when senators voted 61 to 36 to kill the amendment.

Several senators who favor a new AUMF withheld their support for Paul’s amendment for fear of leaving soldiers in combat in a legal lurch if Congress cannot pass an AUMF by the proposed deadline. Those included Sen. Jeff Flake, the leading GOP voice urging a new AUMF, and McCain, his fellow Arizona Republican, who said he also favored drafting a new AUMF through a careful committee process.

“All that we do to defeat al-Qaeda and ISIL rests on this AUMF,” Senate Majority Leader Mitch McConnell (R-Ky.) argued on the Senate floor, using another name for the militant group known as the Islamic State, or ISIS. “We cannot break faith with these brave men and women by removing the authority they rely upon . . . and leave them questioning whether elected officials in Washington understand what they do.”

Senate Foreign Relations Committee Chairman Bob Corker (R-Tenn.) has promised to address the matter on his panel soon. Paul is a member of that committee.

It has been years since senators began clamoring for a new legal authorization that would reflect the military’s evolved focus in combat. Military operations are no longer solely directed against al-Qaeda and Taliban affiliates, as they were in 2001, but now target the Islamic State and other extremist groups, as well.

Nonetheless, the Trump administration has signaled strongly to Congress that it is not interested in a new authorization. In a letter to leading congressional Democrats last week, Defense Secretary Jim Mattis and Secretary of State Rex Tillerson wrote that the administration “opposes the adoption of any measure to revise or repeal the 2001 AUMF and 2002 AUMF” and “affirms that the United States has sufficient legal authority to prosecute the campaign against the Taliban, al-Qa’ida, and associated forces, including against ISIS.”

In that environment, some senators who voted for Paul’s amendment were simply losing their patience with waiting. “I think it is way past time, way past time, for Congress to take this up and for everybody to be on the record,” said Sen. Tim Kaine (D-Va.), who has been one of the Senate’s most consistent agitators for a new AUMF and who co-authored a proposal with Flake that is expected to be at the center of the debate going forward.

It is not clear whether senators will vote with their gut on other upcoming policy amendments or elect to buy the administration more time to wrestle with difficult matters.

The bipartisan team of Sens. Kirsten Gillibrand (D-N.Y.) and Susan Collins (R-Maine) filed a measure early this week to reject Trump’s recently announced ban on transgender troops serving openly in the military. The bill also would require Mattis to complete a report on transgender service members on an accelerated timeline.

Senators in both parties condemned Trump’s decision on transgender troops when he announced it in July and breathed a partial sigh of relief when they learned the next month that Mattis would freeze implementation of the order until Feb. 1 so he could review its potential effect.

The Gillibrand-Collins proposal is not particularly heavy-handed — at the heart of it is an expression that Congress believes decisions on fitness to serve should not be made based on someone’s gender identity. But some senators skeptical of the president’s order may still want to give Mattis more time to complete his review. Should the Gillibrand-Collins bill be successful, it is likely to encounter fierce opposition in the House, which passed a defense bill of its own that must be reconciled with the Senate’s version before it can become law.

Proponents of amendments to increase sanctions against North Korea in light of a spate of recent ballistic-missile and nuclear tests are also likely to face opposition on the Senate floor.

On Monday, Sens. Cory Gardner (R-Colo.) and Edward J. Markey (D-Mass.) filed an amendment to impose a full trade embargo on goods made by North Korean workers and to cut off from the U.S. financial system any firm or bank that does business with Pyongyang. Their effort — one of two prominent proposals to increase sanctions against North Korea — reflects growing consternation among lawmakers who say there is more Congress can do to persuade North Korean leader Kim Jong Un to abandon his nuclear ambitions.

But the heightened crisis has some senators who just weeks ago were eager to stiffen sanctions on North Korea now urging restraint.

Corker has wanted to revisit North Korea sanctions; in July he spoke of his readiness to not only pass stronger mandatory measures but also require that the president seek Congress’s approval any time he wanted to consider removing them. Last week, however, Corker told reporters that the situation with Pyongyang was too “acute” for Congress to risk going it alone without coordinating efforts with the White House.

Senators have also proposed votes on measures to allow for a round of military base closures and to codify and increase parental leave for service members. Such measures are expected to prompt strong debate, within and across party lines.