A primer on the messy U.S. migration debate now spreading everywhere from Ukraine to Canada

The United States is experiencing ahistoric migration surge, and the political fallout is spreading to somefar-flung andunpredictable places.

In Washington, it's pushed the federal government to the verge of a constitutional standoff with Texas, and it could lead to the first impeachment of a federal cabinet member in 148 years.

Outside of the U.S., it's pulling Canada into the debate, and it could evenposean existential threat to Ukraine.

Republicans blame the Biden administration for laximmigration enforcement. The administration countersthat Republicans have been hypocrites, less interested in resolving the issue than in milking it politically.

So what's going on? Here are eight key things to know that help explain the ongoingsituation.

Migration numbers are skyrocketing

The U.S. is seeing a record number of migrant encounters:acatch-all statistic that lumps together people stopped from entering the country for a variety of reasons,from trying to sneak in illegallyto forgetting their passport at home.

There were3.2 million encounters last year, up from less than 500,000a decade ago. Many of these people are quickly expelled;most stay in the U.S.at least temporarilyas they seek asylum or another status.

Asylum cases can drag on for years, and there's a growing backlog. It's depleting public resources as far as New York City, where migrants were temporarily sheltered in a school.

These are just the documented cases.Hundreds of thousands more migrants evade detection and enter the U.S. illegally the administration estimatesthere weremore than 600,000 last year.

The phenomenon is part of a historic worldwide migration surge as peoplearound the globe flee conflict, catastrophe and crumbling states. But while last year's numbers are unprecedented, the U.S. has experienced migration surges in the past including during Donald Trump's presidency in 2019.

"This is not a problem we got in two years, or five years," said Theresa Cardinal Brown, an immigration expert at the Washington-based Bipartisan Policy Center.

There's a push to impeach theHomeland Security secretary

Republicans want to impeach Homeland Security Secretary Alejandro Mayorkas, which would make him the first cabinet member to be ousted this way since 1876.

Their stated rationale is that Mayorkas has broken his oath to uphold the nation's immigration laws. Critics say the real reason is scoring partisan headlines.

A vote could happen next week. There's no guarantee it will pass the GOP-led House, and even if it did, Mayorkas's job seems safe, as Democrats control the Senate.

A defiant Mayorkas points to a recent rise in deportations as proof he's not ignoring laws.

"Your false accusations do not rattle me," Mayorkas wrote in a letter to Republicans, arguing that what the country really needs is a new law, and new funding, to handle modern migration volumes.

Republicans want Biden to reverse hisreversals

Republicans insist President Joe Biden doesn't need a new law. He can start, they say, by undoing 64 actions he took that expanded migration.

In his first days in office in 2021, Biden rolled back several Trump-era policies, including haltingconstruction of the Mexican border wall;restoringrefugee acceptance levels;endinga pandemic pause on immigration processing; and scrappinga travel ban from a group of mainly Muslim countries.

Biden also expanded immigration parole permission to stay in the country temporarily while an application for admission is consideredto record levels. He's used it to grant temporary stays to more than one million peoplewho have either comefrom unstable countriesor successfully obtained an immigration appointment through an app.

Defenders say the parole program isworking well;Republicans fume that immigration parole isonly supposed to be used in rare, specific cases, and now it's being abused.

Cases of so-called "catch and release" are also on the rise: whileapplicants fight asylum cases, they're freed into the general population. Biden has more than doubled the hundreds of thousands of people benefiting from this policy.

In a speech this week,Republican House Speaker Mike Johnson said these policies have created "a catastrophe at the southern border."

"It is because the border has been deliberately opened wide," Johnson said.

However, Biden has been toughening enforcement lately.Expulsions of migrants deemed inadmissible started increasing last year. Meanwhile, in a reversal of an earlier move, Biden is now getting Mexico to retainmoremigrants; in recent weeks, it's resulted in a drop in U.S.-bound migration.

That cross-border co-operation is fragile.

Mexico's president,Andres Manuel Lopez Obrador, is making a series of complex demandsin exchange for furtherhelp. The latest? He wants an apology from the U.S.over a media reportthathis initial presidential campaign was heavily funded by a drug cartel.Barring an apology, he's threatening to stop co-operating on migration.

Venezuela is making similar threats. It's begun accepting some deportation flights but says it will stop if the U.S. reimposes sanctions.

All this underscores a reality rarely acknowledged when American politicians discuss deportation: It takes a willing destination country.

A proposedmigration billis likely doomed

A small, bipartisan group of senators is negotiating a bill to block more migrants. It would give the president new power to close the border when there's a migration surge.

It would also ramp up funding for immigration judges and other officials to decide cases quickly, clearing the years-long backlog.

But all signs point to thebill being doomed. Even if it got the required 60 per cent of the vote in the Senate, the Republican House is calling it a non-starter "dead on arrival" is how Johnson put it in a letter to colleagues.

Progressive Democrats are also complainingas this bill will likely excludetheir long-pursuedgoal: legal statusfor undocumented people.

Meanwhile, Trump has repeatedly made clear that he wants Republicans to stop the bill. Some Republicans tell reporters that Trump, widely expectedto be the next GOP presidential candidate,is communicating privately that he wants the issue to stayunresolvedso he can campaign on it.

Republican Sen. Mitt Romney described Trump's behind-the-scenes behaviour as "appalling," but asmaller number of Republicans have publicly endorsed his logic. Rep. Troy Nehls told CNN that passing a border bill could help Biden's poor approval rating.

"Why would we do anything right now to help [Biden] with that?" Nehls said.

There are complicated logistical challenges

The more common refrain from Republicans is that Biden can simply start acting on his own instead of waiting for Congress to pass a bill:Ifhe reversed some of his immigration policies, it could reduce the number of migrants in the U.S.

But there are complex, possibly insurmountable, logistical challenges.

For example, there are 34,000 beds in detention facilities belonging to Immigration and Customs Enforcement, said Aaron Reichlin-Melnick, policy director at the American Immigration Council.That's far fromenough to house the more than two million people apprehended by border agents last year,let alone house them through a years-long asylum case. So asylum claimants get released into the U.S.

And it's not like the U.S. can just dump asylum claimants anywhere. Other countries canrefuse to take them. Also, border agencies have limited planes and pilots to manage deportationsthe U.S. currently runs six deportation flights per day, Reichlin-Melnick says.

When Cardinal Brown hears people suggest Biden could usehis existing powers to halt irregular migration, she says, "I want to pull my hair out."

She said the solution requires more resources; more co-operation withother countries; more humanitarian aidto house migrantsin their home regions; and more targeting of criminal cartels that traffic migrants.

Even after all that, she said, there would still be some irregular migration.

WATCH | Ukraine's president addresses U.S. Congress:

Ukrainian President Zelenskyy appeals to U.S. Congress for more aid

10 months ago

Duration 2:00

At an in-person visit with U.S. President Joe Biden in Washington, Ukrainian President Volodymyr Zelenskyy made an impassioned plea to Congress for more aid, but skeptical Republicans appear unmoved.

Ukraine is running low on weapons

Biden has been trying for months to replenish Ukraine's weapons stocksas it faces a perilous battlefield shortage. Nationalist Republicans responded with a complaint:Why fundthe defence of Ukraine's borderswhile America's own borders are so porous?

So Biden proposed a solution: lumpingtogether security funding for Israel, weapons transfers to Ukraineand U.S. border measuresinone big security bill.

His logic was that lawmakers would likelier pass the package as a whole. Instead, the whole plan riskscollapsing.

All isn't yet lost for Ukraine. Some pro-Ukraine Republicans, like Sen. Mitch McConnell, are talking about splitting the bill to save Ukraine funding.

A civil cold war is looming with Texas

The country is inching toward a constitutional standoff.

Texas has placed razor wire at one high-traffic border crossingroute, and is refusing to let national authorities access it.

The dispute intensified last month when a migrant woman and two children drownednearby in the Rio Grande.

The Supreme Court ruled that the feds have a right to cut down thefence. In the absence of a legal order explicitly requiring the fence to be taken down, Texas is ignoring the ruling.

Many conservative states support Texas. Their choice of language has been likened by some analysts to the rhetoric before the U.S. Civil War.

"The federal government has broken the compact between the United States and the States," TexasGov. Greg Abbott wrote in a statement.

More eyes are turning to Canada

Irregular migration from Canada is getting new attention from Americanpoliticians. One GOP primary candidate, Vivek Ramaswamy, proposed a northern border wall.

Now a more important Republican is weighing in.

"The northern border's bad, too," Trump said during a recent campaign stop.

Republicans point to the near-doubling in encounters at the Canadian border from 2022 to 2023, including a nearlysevenfold increasealong a stretch of northeastern states.

Worse still, the vast majority of people on terrorism watch lists who are stopped trying to enter the U.S. by landhundreds per yearenter from Canada, not Mexico.

Yet the stats can be misleading if you recall that "encounters" include minor infractions like forgotten passports. When it comes tothe more serious issue of those trying to sneak into the U.S. by crossing between legal checkpoints, the number of those caught arriving from Canada (10,021) was microscopic compared to those arriving from Mexico (more than two million).

It could still grow into a political problem, said Cardinal Brown, who once ran Homeland Security operations at the U.S. embassy in Ottawa.She pointed to Canada's visa policies as a potential friction point.

Nearly half the irregular encounters at the northern border involve travellers from Mexico, who can travel visa-free to Canada but not to the U.S.

The U.S. government has begun pressingCanada to restore its former visa requirements for Mexico.

Reichlin-Melnicksays he can envision that pressure growing. However, he also cautions thatthe numbers from Canada areso "vanishingly small" that they may never get a U.S. president's attention.