From campaigning for a new border wall to cracking down on sanctuary cities, Acting Director of U.S. Immigration and Customs Enforcement (ICE) Thomas Homan says he'll “never back down” from safeguarding the border and advancing President Donald Trump's agenda.

“If you violate the laws of this country, if you enter illegally, which is a crime, it’s not going to be OK anymore,” Horman declared during a speech at the Border Security Expo in San Antonio in early February, adding that he “100 percent support[s] the wall."

In 2017, Homan announced that illegal border crossings were at a 45-year low.

"Under this president, who's now letting us do our job and taking the handcuffs off the men and women of the Border Patrol and ICE, arrests are up," Homan said in an interview on "America's Newsroom" in December 2017.

Trump touted the agency's success in an early-morning tweet on Wednesday.

"45 year low on illegal border crossings this year," the president wrote. "Ice and Border Patrol Agents are doing a great job for our Country. MS-13 thugs being hit hard."

ICE removed 226,000 people from the U.S. in the 2017 fiscal year – down 6 percent from 2016. During the same time period, the agency arrested more than 110,000 people, a 42 percent increase over the previous year.

Here's what you need to know about Homan, and about his priorities as acting ICE chief.

Who is Thomas Homan?

Homan was appointed ICE director, replacing Daniel Ragsdale, in January 2017. He previously served as ICE's executive associate director of enforcement and removal operations (ERO).

A 33-year law enforcement veteran, Homan served as an NYPD officer and Border Patrol agent before holding several positions within ICE, which was established in 2003.

"ICE was created based on the recognition that global threats have become more dangerous, and a new approach was needed to ensure the security of the U.S. homeland and the American people," the agency explains on its website.

Homan was named assistant agent in charge in Dallas after ICE was created. Nearly a decade later, in March 2009, he transitioned to the role of assistant director for enforcement of ERO before being promoted to deputy executive associate director, according to a statement released by the Department of Homeland Security.

In 2015, Homan was given the Presidential Rank Award, which recognizes individuals for "exceptional performance over an extended period of time."

"Thomas Homan deports people. And he’s really good at it," The Washington Post said in an April 2016 profile.

What is Homan focusing on as ICE director?

Stepping up enforcement in sanctuary cities like California

ICE began launching "targeted immigration enforcement operations" in major cities, including San Francisco and Los Angeles, after California became a sanctuary state on Jan. 1.

Homan spoke against the state's decision, calling it a "dangerous policy."

“By passing this bill, California politicians have chosen to prioritize politics over public safety," Homan wrote in a statement, adding that this "deliberately obstructs our country’s immigration laws and shelters serious criminal alien offenders."

ICE agents arrested more than 150 individuals in violation of federal immigration law in the Oakland and Fresno areas during a three-day sweep at the end of February.

Roughly half of those arrested by deportation officers have convictions for assault and battery, crimes against children, weapons charges and DUIs, according to the agency.

Homan believes the raids would have been more successful if Libby Schaaf, the Democratic mayor of Oakland, hadn't warned constituents on Twitter. He estimates about 800 criminal aliens were able to elude capture, and federal immigration agents were put in danger because of Schaaf's alert.

"What she did is no better than a gang lookout yelling 'police' when a police cruiser comes in the neighborhood, except she did it to a whole community. This is beyond the pale," Homan told "Fox & Friends" on Feb. 28.

Schaaf says she doesn't "regret sharing this information," adding that no laws were broken by doing so.

Building a better border wall

Homan has repeatedly said he's "100 percent" behind Trump's proposal to build a border wall along the country's southernmost border.

"The border wall is a good tool," Homan said in an interview on "America's Newsroom" in October. "We have proven it worked. Why would we not want to do it?"

In 2017, illegal immigrants from 140 different countries were deported from the U.S., according to Homan, and he believes a border wall would help protect the country.

“Every place they built a barrier, the illegal crossings decreased significantly,” Homan told FOX Business’ Maria Bartiromo in January.

Making courthouse arrests

In February, Homan signed a policy that sends deportation agents to federal, state and local courthouses to make arrests.

A two-page directive states that ICE agents will enter courthouses only for specific targets, such as convicted criminals, gang members, public safety threats and immigrants who have been previously deported or ordered to leave.

Family, friends and witnesses won't be picked up for deportation, unless there are "special circumstances," according to the agency.

Immigration agents were told to avoid making arrests in non-criminal areas of the court, like family court and small claims, unless it's approved by a supervisor.

ICE reaffirmed its 2014 policy is in place to avoid deportation arrests at "sensitive locations," including schools, day cares, hospitals, places of worship, funerals, weddings and public demonstrations. Courthouses have never been part of that list.

"We're not going to do it in the courtroom, but to me it's safer," Homan said in an interview in November. "It makes sense to arrest a criminal in a criminal courthouse."

The Associated Press contributed to this report.