Sen. Kirsten Gillibrand (D-N.Y.) said Tuesday that she is drafting the amendment with Sen. Susan Collins (R-Maine) to “try to protect the transgender troops” against the order that President Trump issued in July banning them from the military. (Evelyn Hockstein/For The Washington Post)

Two senators are preparing an amendment to challenge President Trump’s announced ban on transgender people serving in the military that they hope to attach to a sweeping defense bill the chamber is set to consider this month.

Sen. Kirsten Gillibrand (D-N.Y.) said Tuesday that she is drafting the amendment with Sen. Susan Collins (R-Maine) to “try to protect the transgender troops” against the order that Trump initially issued via Twitter in July banning them from the military.

In tweets, the president wrote that the government "will not accept or allow Transgender individuals to serve in any capacity in the U.S. Military." Last month, Defense Secretary Jim Mattis froze implementation of the president's policy until the Pentagon can convene experts to help determine how to best carry it out. In an official memorandum, the White House gave Mattis until Feb. 1 to make that determination.

The backlash to Trump's order has been swift and bipartisan — but it is not yet clear what support there will be for Gillibrand's planned amendment. Representatives for Collins and Senate Armed Services Committee Chairman John McCain (R-Ariz.), who is managing the bill, declined to comment for this story.

The entire $700 billion defense bill is also being held up by at least one senator’s objections to let it proceed unless he is promised a vote on an amendment giving Congress a chance to weigh in on the U.S. military’s engagement in conflicts.

“I’m asking for one vote on an amendment to sunset 2001 and 2002 AUMFs,” Sen. Rand Paul (R-Ky.) said Tuesday, referring to authorizations for use of military force. “If I get that vote, I’ll let [the defense bill] go, otherwise I’ll oppose it coming up.”

Both the Trump and Obama administrations have argued, over the objections of many in Congress, that the legal foundation for continuing combat operations in Afghanistan and against the Islamic State can be found in a pair of authorizations for use of military force that Congress passed 15 years ago. The 2001 AUMF authorized military operations against al-Qaeda, the Taliban and associated groups, while the 2002 AUMF let the military go into Iraq.

Paul explained that his amendment would not actually replace the AUMFs he seeks to repeal. Instead, it would “sunset” the existing AUMFs after six months, giving Congress a hard deadline in which to come up with an alternative.

It’s “kind of similar to what they’re doing with DACA,” Paul explained, noting it would “force us to debate on it in the next six months.”

On Tuesday, Attorney General Jeff Sessions announced that the Trump administration would end the Deferred Action for Childhood Arrivals (DACA) program that has let 800,000 undocumented immigrants brought to the United States as children study or work free from fear of deportation. The program will end after six months, however — giving Congress a half-year window in which to try to pass a bill to allow them to stay.

Paul is not the only member of the Senate who has been angling for Congress to pass a new AUMF. Several members of Congress have proposed new AUMFs to replace one or both of those authorizations with a new mandate for fighting terrorist groups. Senate Foreign Relations Committee Chairman Bob Corker (R-Tenn.) has promised that his committee would take up at least one AUMF proposal this year.

But although proponents of a new AUMF think that the defense authorization bill is a good vehicle for a military force authorization, the Senate’s chief agitator for an AUMF said Tuesday that he disagreed with Paul’s approach of holding up the defense bill until a vote is guaranteed.

“The national defense bill is a product of our work across the aisle in the Armed Services Committee to support our troops, and holding that up unnecessarily would be a disservice to our service members and their families,” said Sen. Tim Kaine (D-Va.), who has been angling for a new AUMF for several years. He and Sen. Jeff Flake (R-Ariz.) partnered again this year to write the AUMF proposal that has gained the most traction in the body.

“We do owe it to the public to debate our military engagements in the most transparent way possible, which is why the best approach is for the Foreign Relations Committee to accelerate its work, mark up a new AUMF, and vote on it,” Kaine added.

Paul may not be the only senator objecting to efforts to advance the defense bill through the Senate. On Tuesday evening, Sen. John Cornyn (R-Tex.) said that Sen. Mike Lee (R-Utah) was also resisting moving forward.

Lee spokesman Conn Carroll said Wednesday morning that Lee is “looking for an open debate and opportunity to amend the NDAA,” particularly with a measure to guarantee that American citizens and lawful permanent residents detained during war or other military operations are guaranteed due process. Lee has held up the defense bill in previous years over this measure.

Paul has also held up debate on the defense bill earlier this year. Paul objected to the Senate’s bringing up the defense bill in the immediate aftermath of the failed health-care vote, pushing the debate to September. McCain cast the deciding vote to bring down the health-care bill, a vote that Trump has forcefully complained about since, including during a rally in McCain’s home state of Arizona. But Sen. Lindsey O. Graham (R-S.C.) on Tuesday rejected rumors that anyone might be holding up the defense bill as a means of punishing McCain for that vote.

Senate leaders are trying to make sure that McCain can shepherd the bill through the Senate as he has done in years past, despite the senator’s recent brain cancer diagnosis. McCain returned to Capitol Hill from the August recess with the rest of lawmakers on Tuesday.