U.S. Department of Homeland Security Secretary Alejandro Mayorkas holds a press conference at a U.S. Border Patrol station on Jan. 8, 2024 in Eagle Pass, Texas. (John Moore/Getty Images)

(WASHINGTON) —¬†House Republicans are moving ahead with impeachment proceedings against Homeland Security Secretary Alejandro Mayorkas as they continue to make immigration a key 2024 campaign issue.

House Homeland Security Committee Republicans opened Wednesday’s impeachment hearing against Mayorkas by rehashing familiar arguments that highlight the historically high levels of unauthorized migration across the southern border while Democrats continued to insist the proceedings are a sham.

The hearing comes after a yearlong probe to examine what the committee is calling the secretary’s “failed leadership” as the southwest border experienced a surge of migrants.

Chairman Mark Green, R-Tenn., played clips of Mayorkas discussing “operational control” of the U.S. border, which Congress has previously defined as zero illegal crossings. As Mayorkas has pointed out, under this definition, no administration has achieved operational control. At a previous hearing, Mayorkas said he believed there was a form of operational control and said he was not following the definition outlined in the dated statute.

Even still, Republicans have not identified a specific high crime or misdemeanor that Mayorkas committed. Chairman Green appeared to acknowledge as much.

“Secretary Mayorkas’ refusal to follow the law is sufficient grounds for impeachment proceedings,” Green said.

“The constitutional history is overwhelmingly clear on this subject,” he continued. “The founders designed impeachment not just to remove officials engaged in criminal behavior, but those guilty of such gross incompetence that their conduct had endangered their fellow Americans, betrayed the public trust and represented a neglect of duty.”

Rep. Bennie Thompson, the top Democrat on the House Homeland Security Committee, raised a number of procedural inquires about whether Mayorkas would have the ability to respond to evidence. Green dismissed the claim, saying the committee would “follow the rules of the House.”

Committee Democrats are united that the impeachment proceedings are unwarranted and purely the result of immigration policy disputes.

“It is now campaign season, and Republicans recently rolled out their impeachment proceedings against the secretary like the pre-planned, pre-determined political stunt it is,” Thompson said. “This is not a legitimate impeachment.”

“You cannot impeach a cabinet secretary because you don’t like the president’s policies,” Thompson said. “That’s not what impeachment is for. That’s not what the Constitution says.”

University of Missouri law professor and impeachment expert Frank Bowman, a witness at Wednesday’s hearing, echoed that argument, saying impeachable conduct does not apply to policy disputes or political debates.

“It is instead a measure of last resort reserved as one frame or put in for great and dangerous offenses,” Bowman said. “In other words, official misconduct, which is extraordinarily serious in degree and critically of a type that corrupts or subverts governmental processes or the constitutional order itself.”

Attorneys general of Montana, Oklahoma and Missouri also testified as witnesses. The three Republican leaders said Mayorkas has failed to enforce the law, and alleged he misled Congress when discussing “operational control” at the border.

Green, during a GOP visit to a Texas port of entry last week, accused Mayorkas of having “broken his oath to defend this country” and called him a threat to national security.

Mayorkas defended the administration’s work in his own visit to the Eagle Pass, Texas, entry point on Monday. He said the department’s taken “bold, necessary steps” while Congress has yet to pass legislation.

“Some have accused DHS of not enforcing our nation’s laws,” he said. “This could not be further from the truth.”

Migrant encounters at the U.S.-Mexico border reached a record high in December. Sources told ABC News preliminary data showed there were 302,000 encounters last month.

Border Patrol apprehensions have decreased from the historic level, with agents apprehending about 3,244 migrants daily over the past week, according to internal data obtained and verified by ABC News. This past Sunday, agents recorded 2,729 apprehensions, a sharp decline from the two-decade record of nearly 11,000 in a single day last month.

House Republicans used a trip to the border last week to double down on their demands for tougher immigration restrictions as negotiations continue on a supplemental aid package focused on national security.

President Joe Biden last year laid out a package that included nearly $14 billion for the border to hire more agents and immigration judge teams, while also providing aid for Israel, Ukraine and Taiwan. But Republicans are tying the foreign aid to more sweeping legislative changes when it comes to immigration, such as more restrictive asylum guidelines.

“If President Biden wants a supplemental spending bill focused on national security, it better begin by defending America’s national security,” House Speaker Mike Johnson said.

A group of senators have been working for weeks on finding compromise, and Congress returned to Washington this week after holiday recess. But disagreements over parole provisions has led to increasing pessimism that a deal can be struck by week’s end.

I just don’t see any way to be able to get that done this week,” Sen. James Lankford, R-Okla., said late Monday. “There’s a lot more that needs to get done. It starts speeding up, and they you hit a point that you realize now this is going a whole lot slower.”

Mayorkas has been involved in the negotiations, and said Monday the department needs more Border Patrol agents, case prosecutors, asylum officers and technology to combat the flow of fentanyl.

“We now need Congress to do their part and act,” he said. “Our immigration system is outdated and broken and has been in need of reform for literally decades. On this, everyone agrees.”

Mayorkas has long been a target of Republican ire over the border. The House GOP effort to oust him would be the first potential impeachment of a Cabinet official since Secretary of War William Belknap in 1876, though it’s unlikely Mayorkas would be convicted in a trial in the Democrat-led Senate.

ABC News’ Allison Pecorin and Mariam Khan contributed to this report.

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