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

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If House Republicans can muster the simple majority of votes they need to impeach Homeland Security Secretary Alejandro Mayorkas, it will be an unprecedented moment in US history.

While there was one previous Cabinet official to be impeached by the House, the circumstances of that scandal, featuring Secretary of War William Belknap in 1876, are so different as to defy comparison, except in one way: Belknap was acquitted by the Senate as Mayorkas almost certainly would be.

Belknap was impeached for corrupt kickbacks; Mayorkas faces impeachment for his policy approach

The most important difference between Belknap and Mayorkas is the purpose of their respective impeachment cases.

As everyone should remember from the two impeachments and Senate acquittals of former President Donald Trump, the Constitution’s impeachment clause allows for the removal of a federal official from office and bars that individual from office in the future for “Treason, Bribery, or other high Crimes and Misdemeanors.”

Belknap served during the so-called Gilded Age of US politics, and his crime was the corrupt financing of an extravagant lifestyle in the nation’s capital. He took kickbacks from a person he appointed to lead a trading post in Oklahoma.

The articles of impeachment against Mayorkas, on the other hand, outline policy differences rather than corruption, bribery or another crime. Republicans disagree with the administration’s approach at the border and argue that Mayorkas is not enforcing the laws.

Belknap was impeached unanimously; Republicans may not have the votes to impeach Mayorkas

The House is able to impeach a current or former federal official with a simple majority vote. Lawmakers approve articles that lay out the charges against the official, almost like an indictment. In the case of Belknap, that impeachment vote was unanimous, and the evidence was overwhelming.

The Mayorkas impeachment, on the other hand, is an almost entirely partisan affair, and Republicans may not have the votes to proceed. With a slim GOP majority, Republican leaders who support the impeachment can only afford to lose two or three votes, depending on how many people are absent for the vote and assuming no Democrats cross party lines.

One Republican, Rep. Ken Buck of Colorado, announced Monday he would oppose the impeachment effort because it is a misuse of the practice of impeachment.

“Partisan impeachments that do not meet the constitutional standard will boomerang back and hurt Republicans in the future,” Buck wrote in an op-ed for The Hill. “I can envision a future Republican administration where a Democrat-led House uses this precedent to act against a Republican Cabinet member who isn’t discharging their duties in a way that Democrats desire.”

Another Republican, Rep. Tom McClintock of California, announced on Tuesday he also will vote against impeachment, saying the articles “fail to identify an impeachable crime that Mayorkas has committed.”

Belknap tried to resign rather than be impeached; Mayorkas has Biden’s support

The Senate historian describes Belknap rushing to the White House to resign his position just as the House was scheduled to vote on the impeachment effort. There is a remarkable newspaper illustration of President Ulysses Grant holding Belknap’s hand while Belknap, weeping, turns away.

Belknap burst into tears after handing Grant his resignation.

The House proceeded anyway, according to the Senate Historical Office, and voted for impeachment, accusing Belknap of “basely prostituting his high office to his lust for private gain.”

After all that, Belknap was acquitted; Mayorkas surely would be too

After a House impeaches an official, the Senate can then conduct a trial based on the articles of impeachment, but it requires a supermajority of two-thirds of senators to convict and impeach an individual.

Today, it would require 67 “guilty” votes out of 100 senators, assuming all senators are present. Considering that Democrats maintain a slim majority in the Senate, conviction seems impossible.

In 1876, there were fewer senators: 61 voted in the Belknap trial. Thirty-seven senators voted “guilty,” 23 voted “not guilty for want of jurisdiction” and one voted “not guilty.”

The senators who voted not guilty based on jurisdiction did not question Belknap’s guilt, but rather thought he should not be convicted since he had already resigned.

While there was bipartisan support to oust Belknap, politics were no less divisive in 1876. In fact, that’s the same year a contested presidential election nearly tore the country apart again.

Several states sent conflicting tallies of votes. Congress appointed a Republican-controlled commission to examine the election results, and they essentially handed the White House to Rutherford B. Hayes in exchange for largely ending Reconstruction. Known as the Compromise of 1877, it’s one of the five presidential elections in which the winning candidate got fewer total votes than the loser.