Washington (CNN) Consensus is building in Washington for a deal that would pair border security and a solution for young undocumented immigrants -- but that doesn't mean anything will be easy.

There's a reason the failed 2013 "Gang of Eight" immigration reform bill ended up topping 1,100 pages: Reaching a deal on anything to do with immigration often requires numerous side deals to build a majority of lawmakers, and once those deals start getting made, a bill can grow exponentially.

Although lawmakers are talking about border security and making the Deferred Action for Childhood Arrivals program, or DACA, into permanent law, there are numerous options -- and potential pitfalls -- that still need to be worked out.

Here's a sampling of what Congress has to consider:

Which DACA approach?

For starters, lawmakers will have to agree on the way to approach the fix for DACA -- an Obama-era program that offered protection from deportation to young undocumented immigrants brought to the US as children, along with the ability to work and study. Trump has decided to let the two-year permits issued under DACA begin expiring in six months amid concern about a legal challenge to the program, which was created by executive action.

There are already four different bills introduced in Congress that aim to tackle the issue. Two bipartisan approaches have been proposed by South Carolina Republican Sen. Lindsey Graham and Illinois Democrat Sen. Dick Durbin. One, the BRIDGE Act , would be a three-year protection for individuals eligible for DACA. It would be the narrowest option and would need to be renewed by Congress.

Democrats are insisting on using their other bill -- the Dream Act . First introduced by Durbin nearly 20 years ago, the bill would offer DACA recipients and eligible young people a pathway to permanent residency and potentially citizenship if they study or work in the US. Republicans have been hesitant to support the Dream Act outside of a few co-sponsors, however, partly because of the pathway to citizenship.

More Republicans have lined up behind Florida Republican Rep. Carlos Curbelo's Recognizing America's Children Act, or RAC. Similar to Dream, the bill would set a younger threshold age, by which, immigrants would have had to be brought to the US and sets up five-year periods of conditional permanent residency on the way to an eventual pathway to citizenship. Both bills require background checks and clean criminal records. The bill has more than 30 co-sponsors in the House and is expected to be introduced in the Senate by North Carolina Republican Thom Tillis.

The fourth option, the American Hope Act , was introduced by Illinois Democrat Rep. Luis Gutierrez and has only Democratic co-sponsors, making it the least likely option for the base of a deal. Along with provisions like the other bills, it also would add things like letting states determine residency for higher education.

Further questions still remain for many conservatives, as well. Would naturalized former DACA recipients be allowed to sponsor family members to live in the US? Would legalized immigrants be eligible for federal benefits? Conservatives could balk from any deal without those points addressed.

What does border security mean? A wall?

While virtually all lawmakers support the idea of "border security" in theory, there are wide disagreements over what that should look like.

Trump said in a tweet Thursday that he expects "massive border security" in exchange for a deal on DACA, which he also defended as the right thing to do. Trump and the White House went back and forth on whether that included a border wall, with Trump saying a wall would come "later" and "very soon," but insisting it would get built.

Democrats have uniformly opposed any money that would go to building new border wall, and have told Republicans they will not vote for any government funding bill that includes it.

But even beyond the wall, different approaches to border security remain. House Minority Leader Nancy Pelosi said in a dear colleague letter overnight Thursday that she and her Democratic leadership colleagues have proposed a 2013 bill that passed the House Homeland Security Committee -- a bill that one senior congressional aide called a "nonstarter" in the current environment. That bill mostly called for studies and reports on how to gain operational control of the border.

Texas Rep. Mike McCaul, who still chairs that House committee, and Texas Sen. John Cornyn, also a Republican, have proposed corresponding bills on border security that would pour $15 billion over four years into securing the border, including by building physical barriers. But it also includes pieces that would increase scrutiny of people seeking to legally come to the US, and measures like that could cause Democrats to balk.

Another sticking point involves tracking people who overstay their visa -- a greater contributor to the undocumented population in recent years than people who enter the US illegally. Technological issues have held up the ability to track people exiting the US in addition to entering the US, but lawmakers continue to push for greater policy support for a full entry-exit tracking system nationwide.

Interior enforcement

One of the trickiest arguments facing a deal is how immigration laws are enforced within the US. Many Republicans have been pushing for a deal that would be bigger than simply DACA and some enhanced border security.

"Let's fix the immigration system before we start talking about what we're going to do with the people who are here illegally," said Idaho Republican Rep. Raul Labrador, a member of the House Freedom Caucus and a leading conservative on immigration policy. "The 12 million (undocumented) people that are here, they're just a symptom of a broken system. ... When somebody's bleeding you don't just mop the floor, you have to fix the wound first."

But Democrats are not likely to go along with such an effort.

"We're not going to trade the protection of 'dreamers' for the deportation of others," Arizona Democrat Ruben Gallego said, articulating a Democratic position against any deal that would increase deportations of undocumented immigrants not covered by a DACA fix.

Republicans are aggressive in supporting increased interior enforcement. Trump has called for thousands of new agents for Immigration and Customs and Enforcement, and House conservatives are pushing for a vote on the Davis-Oliver Act, a bill that has passed the House judiciary committee that would include a large number of hard-line enforcement measures, including empowering state and local law enforcement to enact their own immigration laws and penalties, giving the government powers to revoke visas, beef up ICE's ability to arrest and deport undocumented immigrants, increase criminal penalties for undocumented immigrants and punish sanctuary jurisdictions.

The House has yet to vote on the full measure, but has passed pieces of it already as conservatives push for a vote on the full bill.

Sanctuary cities

Another intensely controversial fight remains over sanctuary cities -- a catch-all term used to refer to local jurisdictions that have some policy of noncooperation with federal law enforcement when it comes to immigration.

The Trump administration has made sanctuary cities a prime enemy, attempting to cut off federal funding, especially law enforcement funding, from cities that put in place sanctuary policies. Those efforts have already generated lawsuits, one successfully blocking part of an executive order.

Supporters of such policies, though, including a number of mayors and police chiefs across the country, argue that they allow local law enforcement to have greater trust within communities, a key of safe policing -- and that local jurisdictions shouldn't shoulder the federal government's enforcement responsibilities.

The House has already passed legislation that would allow much greater punishment of sanctuary cities, and require more cooperation with the feds by law. The contentious legislation has an unclear path in the Senate, where Republicans need at least a handful of Democrats to clear procedural hurdles on any bill.

Permanent residency

Trump has also already brought up another potential third rail of the immigration debate as part of the DACA discussion -- reforming legal immigration.

The President has discussed the RAISE Act, a bill from Republican Sens. Tom Cotton of Arkansas and David Perdue of Georgia, which would slash the number of green cards available per year roughly in half. The bill would cut substantially down on family-based green cards and eliminate the diversity lottery, then overhaul the employment-based green card system to give heavy preference to high-skilled, highly educated, English-speaking immigrants. Supporters of the bill argue it could raise US wages -- a key talking point of advocates for restricting legal immigration.

Trump has touted the bill as a possible part of a DACA compromise in private meetings with lawmakers and in public statements about his goals for legislation.

The proposal has met heavy skepticism from the left and the right, mainly because of the overall cut in legal immigration and the fact that the bill would make it near impossible for low-skilled immigrants to obtain permanent residency in the US.

While the concept of merit-based immigration has widespread support -- and the 2013 Gang of Eight bill also included a point system like the RAISE Act -- more consensus exists around higher overall numbers of green cards and a system that picks immigrants based on job needs in the US, not an overall emphasis on a particular skillset.

Temporary visas

Beyond who gets a green card -- lots of lawmakers want changes to the way temporary workers are brought to the US.

Some, especially on the far right, want vast cuts in the number of immigrants allowed to work in the US temporarily each year, as they argue immigrants take jobs from Americans and lower US wages overall.

Most lawmakers, however, support changes to the temporary visa system that would make it easier for businesses to bring in temporary workers with a range of skills, citing consensus among economists that immigration is good for the overall economy and that many jobs would go unfilled by Americans.

Different areas of the US, though, want different pieces. Heavy agricultural states tend to want the ability to bring in workers year-round, as agricultural visas are currently only seasonal and come with heavy strings attached for employers. In bigger tech sectors of the US, visas for highly skilled immigrants are the issue, and the medical industry has argued that it needs more visas to staff hospitals with doctors and nurses all over the US.

Visa reform has eluded lawmakers for years -- and in the Gang of Eight bill, for example, the increase in fees that came from the visa overhaul was needed to pay for the investment in border security piece of the equation.

E-verify

Lawmakers have debated for years about the use of a national mandatory e-verify system, by which any employer would have to verify with the federal government they are employing people legally allowed to work in the US, which undocumented immigrants are not. Employers who then knowingly employ undocumented immigrants could be harshly punished. The House judiciary committee is expected to soon consider a bill that would create such a system.

The proposal faces opposition from industries that rely on undocumented labor as well as immigration advocates who want a solution for the millions of undocumented immigrants that have lived in the US for years.

Deals that have gotten momentum for e-verify in the past have typically come paired with visa reform.