The House is set to vote on whether to impeach Homeland Security Secretary Alejandro Mayorkas on Tuesday, where lawmakers could take the rare step of impeaching a Cabinet official for the first time in nearly 150 years.

House Republicans claim Mayorkas has committed high crimes and misdemeanors for his handling of the southern border, even though several constitutional experts have said the evidence does not reach that high bar.

Even if Mayorkas is impeached in the House, it is highly unlikely that he will be charged in the Democratic-controlled Senate. Senate Democrats are still weighing how to respond if Mayorkas is impeached: Move ahead with a trial, or move to dismiss it quickly given their view that it’s blatantly political.

The impeachment effort comes as House Republicans have faced building pressure from their base to hold the Biden administration accountable on a key campaign issue: the border.

But Republicans can only lose three votes in their razor-thin majority if all lawmakers are present, and a handful of lawmakers have not indicated how they plan to vote. GOP Rep. Ken Buck of Colorado announced in an op-ed that he would not vote to impeach Mayorkas. GOP Rep. Tom McClintock of California wrote on X on Tuesday he also will vote against impeaching the DHS secretary.

House GOP Majority Whip Tom Emmer told CNN on Monday he is confident Republicans have the votes to impeach Mayorkas.

“We’re whipping Republican votes,” Emmer said. “I’m confident we are going to pass it.”

Only one Cabinet official has previously been impeached in American history: Secretary of War William Belknap in 1876.

House Homeland Security Chairman Mark Green of Tennessee, who has led the impeachment effort, has been meeting with some of the remaining GOP holdouts in the lead up to the vote, according to GOP sources.

While Republicans in the House argue that the remedy for fixing the crisis at the southern border is to impeach Mayorkas and pressure President Joe Biden to take more executive action, their counterparts in the Senate have worked with their Democratic colleagues to unveil a border deal that would make long-anticipated changes to immigration law. But House Speaker Mike Johnson declared the Senate deal “dead on arrival” in the House after the text was released Sunday evening.

While Republicans have been investigating Mayorkas’ handling of the border since they reclaimed the House majority, momentum to plot a swift impeachment of the secretary picked up steam last month as key swing-district Republicans expressed fresh openness to the idea amid a recent surge of migrant crossings at the southern border.

Green has argued Mayorkas’ “willful and systemic refusal to comply with the law” and “breach of public trust” amounts to the impeachable offenses of high crimes and misdemeanors. Green claimed Mayorkas has “willfully exceeded” his parole authority, “refused to comply” with detention mandates, and lied for saying that DHS has “operational control” over the border. He cited Supreme Court Justice Samuel Alito, who said Congress could “employ the weapons of inter-branch warfare,” including impeachment, in light of the Supreme Court ruling that states could not challenge federal immigration law.

But a variety of legal scholars have poured cold water on the legal arguments Republicans are using to support their impeachment effort.

Alan Dershowitz, who represented former President Donald Trump in his first impeachment, said House Republicans do not have the evidence to impeach Mayorkas.

“Whatever else Mayorkas may or may not have done, he has not committed bribery, treason, or high crimes and misdemeanors,” Dershowitz wrote in an op-ed.

Former DHS Secretary Michael Chertoff, who served under Republican President George W. Bush, constitutional law expert Jonathan Turley, who has been called by Republicans to serve as a witness in hearings, and 25 law professors have all written about why Republicans have not presented evidence against Mayorkas that rises to the level of impeachment.

Mayorkas – whom the department said is meeting with staff in Mountain View, California, on Tuesday, to discuss cybersecurity and artificial intelligence – sent a letter to House Republicans to defend his record in public service.

“My reverence for law enforcement was instilled in me by my parents, who brought me to this country to escape the Communist takeover of Cuba and allow me the freedoms and opportunity that our democracy provides,” Mayorkas said.

Mayorkas wrote that “the problems with our broken and outdated immigration system are not new,” and called on Congress to help provide a legislative solution to the “historically divisive issue.” He praised the bipartisan group of senators he has worked with for its willingness to put their differences aside to try to find solutions at the border.

The Department of Homeland Security has also blasted House Republicans over its upcoming committee vote, calling it a “farce” and “distraction from other vital national security priorities.”

In a memo, DHS slammed the impeachment inquiry, arguing that there are no high crimes or misdemeanors, that the probe was “predetermined from the start” and that the process is “cynical and hypocritical.”

In response to Republicans blaming Mayorkas for the uptick in border crossings, the DHS memo states, “This Administration has removed, returned, or expelled more migrants in three years than the prior Administration did in four years.”

Addressing the claim that Mayorkas has failed to maintain operational control over the border, DHS said that based on the way the law defines operational control, “no administration has ever had operational control.”

Democrats on the Homeland Security Committee have repeatedly bashed their Republican colleagues for their efforts to impeach Mayorkas and have released a report calling the GOP effort “a sham.”

Meanwhile the White House issued a statement calling the resolution to impeach Mayorkas “an unprecedented and unconstitutional act of political retribution that would do nothing to solve the challenges our Nation faces in securing the border.”

Instead of formally launching an impeachment inquiry with a House floor vote, the GOP effort to impeach Mayorkas has been unilaterally run through the Homeland Security Committee as opposed to the House Judiciary Committee, where impeachment articles typically originate, though it is not constitutionally required.

In the investigative phase, Homeland Security Committee Republicans held 10 hearings, published five interim reports and conducted 11 transcribed interviews with current and former Border Patrol agents. But since launching the inquiry, the GOP-led panel has held only two hearings and has decided to move forward with impeachment articles without giving the secretary an opportunity to testify.

Republicans invited Mayorkas to testify at an impeachment hearing on January 18. But the DHS secretary said he was hosting Mexican Cabinet members to discuss border enforcement, and he asked to work with the committee on scheduling a different date, according to a letter obtained by CNN.