The Republican-controlled House voted Tuesday to impeach Homeland Security Secretary Alejandro Mayorkas over the Biden administration's handling of the U.S.-Mexico border.

The vote marks the first time in nearly 150 years that a Cabinet secretary has been impeached.

House Republicans have spent months investigating the secretary's actions as they've aimed to make immigration and border security a key election issue.

Here's a look at how the House arrived at the impeachment vote and what could happen next:

Wait ... didn't they vote on this last week?

Yes. House Republicans tried to impeach the secretary on Feb. 6 but failed. With Democrats united against the effort, Republicans needed every vote they could muster from their razor-thin majority. But in a rowdy, dramatic evening Republicans fell short, with three Republicans voting against the measure. A fourth flipped his vote from yes to no in a tactical move that allowed the impeachment issue to be revisited, so the final vote was 214-216.

But Republicans vowed to bring the impeachment vote back again.

What's going on at the border?

Migrants have long come across the southern U.S. border looking for a new life in the United States, but not like what's happening now. Arrests for illegal border crossings from Mexico reached an all-time high in December. In fiscal year 2022, Border Patrol encountered 2.2 million people crossing the border illegally. You have to go back decades to see comparable numbers.

Statistics aren't always a perfect measure, though, and they can change. The numbers from the 1990s and 2000s are considered vast undercounts because migrants sought to evade authorities as they entered the U.S. And after the dramatic highs of December, the numbers fell by half in January.

Decades ago, the typical migrant trying to come to the U.S. was a man from Mexico looking for work, and he tried to dodge Border Patrol agents. That dynamic has changed drastically. Migrants now are still coming from Central and South America but they're also coming from much farther away — China, Afghanistan and Mauritania, to name just a few countries. And they're often seeking out Border Patrol agents in an effort to seek protection in America.

The numbers have at times overwhelmed the ability of border officials to handle, leading to temporary closures of border crossings so officials can process migrants.

They have also had repercussions far from the border. Migrants going to cities like Chicago, New York, Boston and Denver have strained city services, leading to Democratic officials pushing the administration to take action.

What do Republicans say?

Republicans have laid the blame for all of this on the Homeland Security secretary and said that because of it, he needs to go. They say the Biden administration has either gotten rid of policies that were in place under the Trump administration that were deterring migrants or that the Biden administration implemented policies of its own that have attracted migrants.

The House Homeland Security Committee has been holding hearings over roughly the last year where Republicans have repeatedly lambasted Mayorkas. Witnesses have included an Arizona sheriff, families who have lost loved ones to the fentanyl crisis, experts on constitutional law, and former Homeland Security officials who served under former President Donald Trump.

U.S. House Republicans say the secretary is violating immigration laws by not detaining enough migrants and by implementing a humanitarian parole program that they say bypasses Congress to allow people into the country who wouldn't otherwise qualify to enter. And they allege that he's lied to Congress when he has said things like the border is secure. All of this together, they argue, has created a prolonged crisis that is having repercussions across the country, is squarely the secretary's fault and warrants impeachment. However, the three House Republicans who voted against impeachment argued that the charges didn't meet that bar.

What do Mayorkas, his supporters and others say?

Democrats and many legal experts have said that this is essentially a policy dispute and that Republicans just don't like the immigration policies that the Biden administration, via Mayorkas, has implemented. That's an issue for voters to decide, not an issue that meets the level of "high crimes and misdemeanors" required to impeach a Cabinet official, they argue.

"That one congressional party disapproves, even disapproves vigorously, of President Biden's policies on immigration or other matters within the secretary's purview does not make the secretary impeachable," testified University of Missouri law professor Frank O. Bowman during a January committee hearing.

Mayorkas and his supporters have often said that it's not the actions of the administration that are drawing migrants to the southern border, but that it is part of a worldwide phenomenon of migrants, driven by political, economic and climate turmoil, who are more willing to embark on life-threatening journeys to seek out a better life.

They argue the administration has tried to deal with the chaos at the border. Over roughly the last year, Mayorkas has been the public face of a policy that seeks to create pathways for migrants to come to the U.S., such as an app that lets them schedule a time to come to the border and seek entry. And, they argue, that policy has new efforts to limit who can get asylum and to order aggressive deportations.

But the Biden administration and supporters contend that the secretary is dealing with a wildly underfunded and outdated immigration system that only Congress has the power to truly fix. So far, they argue, it hasn't.

What happens next?

Mayorkas still keeps his job. It's the Senate that decides whether an impeached official is convicted and thus ousted from their position.

But conviction is a much higher bar than impeachment, and Democrats control the Senate 51-49. Two-thirds of the Senate must vote to convict as opposed to the simple majority needed to impeach in the House. That means all Republicans as well as a substantial number of Democrats would have to vote to convict Mayorkas — a highly unlikely scenario considering some Republicans are cool to the idea of impeachment.

Mayorkas has said he's ready to defend himself in the Senate if it comes to a trial. And in the meantime, he says he's focused on his job.