Congress is bracing for several fights this fall over immigration and border security as the Trump administration struggles to make good on its campaign promises. 

The battle could pit President Trump against moderates and senators up for reelection in 2018, who want a more comprehensive approach to both issues.

Lawmakers must pass legislation by the end of September to avoid a government shutdown. The White House appears poised to use that deadline as leverage to secure progress on its immigration agenda — and particularly on funding for a border wall, Trump’s most famous campaign promise.

House Republicans fired the opening salvo before leaving town for the August recess, tucking $1.6 billion for a U.S.-Mexico border wall into a broader $827 billion national security-themed package. But that bill is largely considered dead on arrival in the Senate.

The Trump administration is making a hard push for border wall funding as part of any agreement.

Marc Short, a top White House aide, recently pitched congressional staff on including some border wall funding that would be used for a “double fence” in exchange for more spending on domestic programs — a top priority for Democrats, according to Politico. 

Asked about the potential trade-off, two Senate Democratic aides said “no official offer has been made” but predicted any border wall funding wouldn’t pass muster with Democrats as well as some Republicans.

“If it were made, we expect this misguided wall would be opposed by Republicans as well as Democrats,” said Jay Tilton, a spokesman for Sen. Patrick LeahyPatrick Joseph LeahyOvernight Regulation: Massachusetts AG sues Equifax | Trump weighs easing rules on gun exports | EPA nominee to fight worker safety rule in court Trump to ease rules on gun exports: report Overnight Defense: Senate passes 0B defense bill | 3,000 US troops heading to Afghanistan | Two more Navy officials fired over ship collisions MORE (Vt), the top Democrat on the Senate Appropriations Committee.

A White House spokesperson did not respond to a request for comment.

The battle over the wall could also be pushed until later in the year if lawmakers pass a short-term continuing resolution that would put government funding on autopilot through December. That scenario is viewed as increasingly likely despite opposition from some Republicans. 

Despite broad support in the GOP for increased border security, not everyone thinks the emphasis should be on building a wall.

Top lawmakers in the upper chamber, including Senate Majority Whip John CornynJohn CornynGun proposal picks up GOP support House bill set to reignite debate on warrantless surveillance Republicans jockey for position on immigration MORE (R-Texas), are backing a years-long border security plan that would instead pay for fencing and increased technology.

The legislation — which pairs a crackdown on illegal immigration with increased border security — would cost $15 billion over four years. 

Asked about a potential shutdown fight over the border wall and if Republicans could say they made good on their promise to secure the border without the money, Cornyn told reporters that he didn’t “want to put the cart ahead of the horse.” Still, he said, “the funding should come following a plan, not the other way around.”

“What we're trying to do here is take that fight off the table, talk about a comprehensive plan that will actually work and accomplish the goals that the president has set out,” Cornyn said. 

Though Republicans began fast-tracking Cornyn's bill to the Senate calendar before leaving for the August recess, it could still be referred to a committee once lawmakers return.

A spokeswoman for Cornyn said on Monday that she didn’t have any scheduling announcements.

Meanwhile, some GOP lawmakers are signaling they want to work with Democrats on broader immigration legislation. 

Sen. John McCainJohn Sidney McCainRubio asks Army to kick out West Point grad with pro-communist posts The VA's woes cannot be pinned on any singular administration Overnight Defense: Mattis offers support for Iran deal | McCain blocks nominees over Afghanistan strategy | Trump, Tillerson spilt raises new questions about N. Korea policy MORE (R-Ariz.) wants to try to revive bipartisan comprehensive immigration talks with Senate Minority Leader Charles SchumerCharles (Chuck) Ellis SchumerOvernight Health Care: Schumer calls for tying ObamaCare fix to children's health insurance | Puerto Rico's water woes worsen | Dems plead for nursing home residents' right to sue Crying on TV doesn't qualify Kimmel to set nation's gun agenda Trump knocks ‘fake’ news coverage of his trip to Puerto Rico MORE (D-N.Y.). The two senators worked on a comprehensive immigration reform bill in 2013 that passed the Senate but died in the House.

But while a bipartisan deal would boost their chances of getting an immigration bill through the Senate, it would likely be a non-starter with House conservatives, who are focused on improving border security first.

Another X-factor in the immigration debate is Deferred Action for Childhood Arrivals (DACA), a program that allows undocumented immigrants brought into the country as children to remain here legally. Under DACA, nearly 800,000 undocumented immigrants were given a work permit and protected from deportation. 

Trump vowed to end the program during the campaign. Unless he halts the program by Sept. 5, DACA will be challenged in court — and the administration has not said whether it will defend it. If the administration does not defend DACA, it will effectively be ending it.

Several lawmakers are pushing to ensure that DACA remains in place.

Sens. Dick DurbinRichard (Dick) Joseph DurbinGun proposal picks up GOP support Durbin: I had 'nothing to do' with Curbelo snub Republicans jockey for position on immigration MORE (D-Ill.) and Lindsey GrahamLindsey Olin GrahamDurbin: I had 'nothing to do' with Curbelo snub Republicans jockey for position on immigration Overnight Health Care: House passes 20-week abortion ban | GOP gives ground over ObamaCare fix | Price exit sets off speculation over replacement MORE (R-S.C.) have teamed up on two bills aimed at allowing undocumented immigrants brought into the country as children to remain here legally, at least temporarily.

GOP Sens. Jeff Flake (Ariz.), Dean Heller (Nev.) and Lisa Murkowski (Alaska) have signed on to at least one of Graham’s bills.

Even though the White House has rejected the DREAM Act, a bill establishing a path to permanent residency for undocumented minors, Democrats are continuing to push the proposal as a first step to getting comprehensive immigration through Congress. 

“I think there is some bipartisan support for solutions to this issue,” Sen. Kamala Harris (D-Calif.), who is increasingly the subject of buzz about a presidential run in 2020, said on Monday. “But we frankly need to get more Republicans on board.”

Meanwhile, even as Republicans debate what to do about illegal immigration, Trump is publicly throwing his full support behind a bill from GOP Sens. Tom CottonTom CottonHouse bill set to reignite debate on warrantless surveillance Republicans jockey for position on immigration The Hill's 12:30 Report MORE (Ark.) and David Perdue (Ga.) that would tighten legal immigration by creating a “merit-based” points system and limiting the number green cards awarded each year.

But that bill has generated opposition in both parties. Asked about the legislation, Sen. Marco RubioMarco Antonio RubioOvernight Defense: Tillerson, Trump deny report of rift | Tillerson says he never considered resigning | Trump expresses 'total confidence' in secretary | Rubio asks Army to kick out West Point grad Rubio asks Army to kick out West Point grad with pro-communist posts GOP establishment doubts Bannon’s primary powers MORE (R-Fla.) told a Florida CBS station, "I think the White House knows that you don't have 60 votes for that in the Senate."

The remarks got him quick pushback from conservatives, including members of the Federation for American Immigration Reform, which asked whether GOP leadership was waving “the white flag on real immigration reform.” 

Asked about criticism from his GOP colleagues, Cotton told KARK, an Arkansas-based TV station, that “many of my colleagues are emotional and opinionated yet uninformed” about his legislation and immigration more broadly.

“Congress has tried and failed to pass big sweeping comprehensive reform for 11 years now at least. I just don’t think that’s the right approach anymore,” the GOP senator said in a separate interview.

Both Cotton and Perdue have said they are open to negotiating across the aisle. There are 10 Senate Democrats running for reelection in states Trump won in 2016, and those members could face pressure to support tougher immigration laws.

The Cotton-Perdue bill will need to clear the Senate Judiciary Committee — which includes skeptics such as Graham, Flake and Democrats — in order to move forward.

“More likely ... we’ll have to make some compromises with Democrats and their priorities,” Cotton said. “Even though it’s a bit of a novel approach to the problem, something that hasn’t been debated a lot in Washington, our legislation is designed to address concerns that a lot of Democrats share.”

This story was updated at 11:01 a.m.