US Senate releases deal on border and Ukraine - but will it ever become law?

US senators have unveiled a long-awaited bipartisan deal that aims to combat illegal immigration at the US-Mexico border - and in return grant new aid to Ukraine and Israel.

The Democratic-led chamber will vote on the bill this week, but it appears doomed to fail in the Republican-led House of Representatives.

Joe Biden endorsed it as "the toughest and fairest" border reforms in decades.

Over 6.3 million migrants have entered the US illegally under his watch.

The record-high influx is one of the biggest political headaches facing the president in his re-election bid.

Immigration has emerged as the top issue driving Republicans to the polls in support of former President Donald Trump, the front-runner to face Mr Biden in the November general election.

Faced with mounting public anger over the migrant inflows, President Biden vowed in January to "shut down the border right now and fix it quickly" if Congress sent a bill to his desk.

The deal - which senators have spent months negotiating - is worth nearly $120bn. It allocates $20bn to addressing border security - a key demand of Republicans - and $60bn to Kyiv as requested by the White House. It also includes humanitarian assistance for Gaza and security assistance for Israel.

But even before legislative text of the bill had been released, several Republicans - under pressure from Mr Trump - said they would oppose the measure.

Failure to reach a lasting agreement may leave Mr Biden vulnerable to further attacks on his handling of border security and may see Mr Trump blamed for blocking long-overdue reforms in exchange for an electoral wedge issue.

Since President Biden took office in January 2021, more than 6.3 million migrants have been detained crossing into the US illegally between points of entry, according to statistics from the Department of Homeland Security, or DHS.

Of these, about 2.4 million were allowed into the US, where the majority wait for immigration court dates in which they can make a case for asylum.

While the unparalleled figures ebb and flow on a month-to-month basis, the number of migrant "encounters" reached over 302,000 in December, the highest monthly total ever recorded.

A January poll conducted by CBS - the BBC's US partner - show that nearly half of Americans view the situation at the border as a crisis, with 63% saying that the administration should adopt "tougher" policies.

More than two-thirds of Americans, or 68%, said they disapprove of Mr Biden's handling of the issue.

"Immigration is [Biden's] Achilles' heel. He is right up against the ropes on this," said Tony Payan, the director of the Center for the United States and Mexico at Rice University's Baker Institute in Texas.

"The Republicans have been very successful at maintaining the issue on the headlines, and tying Biden to what they term 'chaos' on the border and an 'invasion' of migrants."

Mr Payan added that the president "is fully aware that this is the most important weakness of his campaign going into the Fall 2024 election".

"He will do anything to keep this off the headlines," he added. "The President wants to get re-elected, and immigration is in his way."

The agreement will, in the words of Republican negotiator James Lankford, move from the current system of "catch and release" to one where migrants are detained and deported.

Senator Lankford brokered the deal with Democratic colleague Chris Murphy and independent colleague Kyrsten Sinema over several months.

Among the most significant changes in the deal is a new federal authority that mandates a complete shutdown of the border when migrant crossings pass a threshold of 5,000 in a week.

In practice, this would mean that migrants who arrive in the US illegally would no longer be allowed to request asylum, and would be deported shortly thereafter - a dramatic reversal of current practiced under US law.

"If given that authority, I would use it the day I sign the bill into law," Mr Biden said in January.

Adam Isacson, a migration and border expert from the Washington Office on Latin America, told the BBC that the change would mark a "radical" departure from current norms and instead harken back to Title 42, a pandemic-era policy of the Trump administration that allowed for the rapid expulsion of migrants.

Other reforms included in the deal are fast-tracked decisions on asylum cases, limits on humanitarian parole, expanded authority to remove migrants from the US, stricter consequences for illegal crossings and even $650m to build or reinforce miles of border wall.

Collectively, Mr Isacson said these measures would have, not long ago, been largely considered unthinkable in US politics.

"Before Donald Trump, we never heard proposals like this in the mainstream debate over the border and migration," he said.

"It was something that maybe people on the anti-immigrant fringe proposed. It really shows how much the window has shifted."

If it passes, the bipartisan compromise would mark the first substantial overhaul of US immigration law since 1990.

In endorsing the deal on Sunday, Mr Biden said: "It would give me, as president, a new emergency authority to shut down the border when it becomes overwhelmed."

"Get it to my desk so I can sign it into law immediately."

The bill needs at least 60 votes to advance through the 100-member Senate.

But widespread opposition to the deal among House Republicans means that the immigration bill is unlikely to ever become law.

Even before its details were announced, House Speaker Mike Johnson warned that the deal would be "dead on arrival" in the chamber.

On Sunday, he again claimed the bill did not go far enough and that Mr Biden should instead use existing laws or executive action to secure the border.

The ossifying Republican opposition has prompted Democrats to accuse Mr Johnson and others of bowing to pressure from Mr Trump, who has urged his Capitol Hill allies to kill the bill.

"Call it the "stupid bill" and make sure it doesn't get passed," the ex-president wrote on his Truth Social platform on Wednesday, claiming the deal "will make things MUCH WORSE".

While Mr Johnson has called the claims "absurd", experts say that Mr Trump's outsize influence has clearly cast a shadow over the negotiations - leaving the Biden administration with few options.

"If they have no new money, and no new tools, even bad ones, then it's the status quo," Mr Isacson said. "That sort of status quo, of letting the Biden administration twist in the wind, is exactly what the Trump campaign wants. They want more B-roll of chaos during the campaign."