When the Obama administration pushed through the Deferred Action for Childhood Arrivals program in 2012, then-Sen. Jeff Sessions was not pleased.

"With its announcement today, the Obama administration has openly declared to the American people that it is determined to contravene the immigration laws of the United States, circumventing the will of the people and authority of its representatives in Congress. In fact, this policy is far broader than the version of the DREAM Act rejected by Congress on a bipartisan basis and contains almost no enforceable limits and requirements," the lawmaker from Alabama said in a June 15, 2012, statement.

Sessions, one of the earliest supporters of President Trump's campaign in 2016, was picked to take over the helm of the Justice Department. Since taking on the role as the nation's top law enforcement officer, he has been turning many of Trump's campaign promises into concrete policies.

Rescinding DACA -- not to mention the fact that Sessions was the one to formally announce it -- was no surprise to several people who know him from his days as a senator.

"You can't understand Jeff Sessions if you don't understand his rock solid commitment to the rule of law and the Constitution," a longterm former Sessions aide told the Washington Examiner in a phone interview. The aide requested anonymity to speak candidly.

According to the aide, Sessions "greatly lamented" about what he saw as the "politicization" of the Justice Department under the Obama administration. So combining that with his "deep passion and love" for the department made becoming attorney general an ideal fit.

"Regardless of the policy, he saw DACA as a grave threat to the constitutional separation of powers," the aide said, adding Sessions was worried such a precedent could have been set "endorsing such powers they could be used to effect numerous policy changes never approved by Congress."

Another former Sessions aide told the Washington Examiner that in addition to the DACA policy in general, he was more so concerned "how the policy was put into place."

"But the notion that the president would just take it upon himself to enact by fiat what the Congress had repeatedly rejected, that was unacceptable to him," the aide said.

Sessions' showed strong opposition to the bipartisan Gang of Eight's immigration reform bill in 2013. Though the bill passed in the Senate despite Sessions' objections, it failed in the House.

Instrumental to that opposition was Stephen Miller, who worked for Sessions as his communications director. Miller now works as Trump's senior policy adviser.

Sessions has long been an "anti-immigration" hardliner for years, Ilya Somin, a professor of law at George Mason University, told the Washington Examiner.

"News reports suggest that he indicated he would refuse to defend DACA in court if Trump had decided to keep it in place," Somin explained. "I would not be at all surprised if it turns out he was working behind the scenes to end DACA, and was a key figure in the administration's decision."

Elizabeth Cohen, a professor at the Maxwell School of Citizenship and Public Affairs at Syracuse University said Sessions' "primary goal of his political tenure has been to crack down on immigrants."

"He has set DACA in his sights and this is likely not the last anti-immigrant gesture he will make as Attorney General," she told the Washington Examiner.

Former federal prosecutor Renato Mariotti noted that Sessions opposed the DREAM Act in 2010, helping to defeat it, which lead to Obama pushing through DACA.

"[Sessions'] role in ending DACA was the continuation of the views he championed for years," Mariotti, who is now a partner at Thompson Coburn LLP told the Washington Examiner.

On Tuesday, Sessions announced the end of DACA from the Justice Department in Washington. He also said he had sent a letter to the Department of Homeland Security recommending the end of the program, calling it "an open-ended circumvention of immigration laws" and "an unconstitutional exercise of authority by the Executive Branch."

The Obama-era program shields nearly 800,000 illegal immigrants who came to the U.S. as children from deportation through a two-year work permit. Now, Congress has a sixth-month deadline to pass legislation to protect the young immigrants.

"Do your job" with DACA, Trump tweeted on Tuesday, referring to Congress.

During his presidential campaign, Trump referred to DACA as "illegal amnesty," but earlier in the year he said he would deal with the issue "with heart," giving some DACA supporters hope he wouldn't rescind the program.