As president, Donald Trump can move swiftly to gut President Obama's signature immigration policies by ramping up deportations and ending a program that has given temporary work permits to immigrants brought to the country illegally as children.
Nearly a third of the 742,000 so-called Dreamers — those given protection under the Deferred Action for Childhood Arrivals program — live in California and are potentially at risk of losing legal status.
Using the same executive authority that Obama claimed to create DACA and other initiatives, Trump also can quickly fulfill his promises to severely restrict the number of refugees admitted each year and to effectively bar visitors from countries with large Muslim populations.
Trump said Thursday, after meeting with Obama at the White House and Congressional leaders on Capitol Hill, that immigration and border security would be among his top priorities when he takes office in January.
"People will be really, really happy," he said. Asked if he would work with Congress to ban Muslim immigrants, Trump walked away without answering.
Trump's aides have begun drafting instructions that he can issue on his first day in office for the nation's 5,000 deportation officers to begin rounding up more people for removals, according to two advisors to his transition team.
"There is vast potential to increase the level of deportations without adding personnel," said Kris Kobach, the Kansas secretary of state and a member of Trump's immigration policy transition team.
By giving more authority to Immigration and Customs Enforcement agents, Trump easily could boost deportations by more than 75% in his first year in office, Kobach said.
That would meet the record set in 2012, at the end of Obama's first term, when more than 400,000 people were deported. It fell to 235,00 last year after illegal immigration fell, and after agents were ordered to focus first on deporting criminals, repeat immigration violators and recent arrivals.
Under Trump, Kobach said, agents likely will return to raiding workplaces and checking workers' status. That practice roiled immigrant communities in the final two years of George W. Bush's presidency and was stopped when Obama came to office.
Trump may find it far more difficult to fulfill other prominent promises, however. They include building a tall wall along the entire border with Mexico and deporting millions more people.
Both proposals would require major appropriations from a Republican-led Congress that wants to cut spending, not increase it. It would require hammering out deals with Democrats who fiercely opposed Trump's proposals on the campaign trail.
Trump has said the wall could cost up to $12 billion to build. An analysis published by MIT Technology Review estimated the cost at $38 billion, nearly the entire annual budget for the 22 federal agencies in the Department of Homeland Security.
Similarly, the cost of forcibly finding, arresting, detaining and ultimately flying or busing millions of people out of the country would be sizable; it would depend on how many and how fast.
A recent surge in families from Central America illegally crossing the border, for example, means the 40,000 beds in detention centers are full. Additional space would require additional funding.
Kobach argued that construction of a border wall could begin quickly. The Homeland Security Department already has authority to build physical barriers and structures on the border and doesn't need permission from Congress, he said.
Next year's budget for U.S. Customs and Border Protection, the parent agency for the Border Patrol, includes $175 million for "procurement, construction and improvements." Even if that money is diverted to the wall, it wouldn't go very far in a multibillion-dollar project.
"Once the building is beginning on a very large scale, there would almost certainly need to be larger appropriation or a shift in dollars," Kobach said.
Mexican officials have adamantly rejected Trump's declaration that Mexico will agree to pay for the wall.
Whether Trump has leverage is unclear. He has touted the fact that Mexican workers in the United States transfer $24 billion in earnings back home each year to help their families.
Trump's supporters have floated a proposal to impose a fee on remittances from people not authorized to work in the U.S., though it's not certain how that would work.
With his pen the president can reduce or slow down the process by which Mexicans get travel cards and visitors' visas. But that could backfire by hurting businesses and tourism near the border.
Republican lawmakers previously have drafted bills to increase spending on border security and to force business owners to check immigration status of new hires on a federal database, among other requirements.
With the GOP controlling Congress, similar bills could make it to Trump's desk. Democrats in the Senate would probably use their filibuster to block the most onerous requirements, however.
The number of refugees admitted to the country can also be trimmed dramatically during Trump's first months in office.
He can reduce the maximum number of refugees admitted from each country as well as change the procedures for screening them, according to Stephen W. Yale-Loehr, a professor of immigration law at Cornell Law School.
A 21-step screening process for refugees who face ethnic or religious persecution, or who fit into other legal categories for protection, already takes more than a year.
"I don't know what anyone could do to make it longer and more onerous than it is right now, but we'll see if he comes up with something," Yale-Loehr said.
Trump also could change regulations to deter companies from hiring skilled foreign workers, such as raising wage requirements for H1-B visa recipients, although it would take time.
"It's a big bureaucracy, and particularly when it comes to agency regulations, the process of getting new regulations through is extremely long and complex," Yale-Loehr said.
Under Obama, the Senate passed a bipartisan bill in 2013 that would have opened a pathway to legal status for immigrants in the country illegally and boosted spending for border security, but the House killed the bill without a hearing.
Unable to win comprehensive reforms in Congress, Obama then resorted to issuing executive actions. In many cases, Trump can reverse them with the stroke of a pen.
He is almost certain to end the DACA program, Obama's signature immigration initiative to protect immigrants who were brought to the country illegally as children.
As of June about 742,000 people — mostly Mexican-born — had qualified for protection under DACA, according to Homeland Security figures. About 29% of them live in California.
"It's a new world." said Roy Beck, the head of Numbers USA, a Virginia-based group that advocates reducing legal immigration levels. Rolling back DACA is "a pretty good start," he added.
When immigrants submitted to background checks under DACA, the paperwork assured applicants their information would not be used to deport them later. But the assurance is not legally binding.
That has stoked widespread fear in immigrant communities.
Maria Pacheco, 21, was brought to Ohio illegally from Mexico as a toddler. Since she received a two-year work permit under DACA, she's been able to get a driver's license, buy a car and work as a pizza shop cashier on the outskirts of Cleveland. Her boss wants her to be a manager.
"When people say, 'Go back to your country,' I don't know my country," she said by phone Thursday. "I've been here since I was 4. This is my home."
She hopes Trump will allow immigrants like her, who work and pay taxes, to stay. Her work permit expires next year, and she fears she won't be able to find a job or keep her car.
"He's a businessman. Maybe he can find a way to keep all these kids working," she said. "Maybe he can look at it in a business way."
Follow me @ByBrianBennett on Twitter