By Anthony ZurcherNorth America correspondent
Getty ImagesMigrants have overwhelmed the town of Eagle Pass, Texas, in recent weeksThe recent surge of migrants crossing the US-Mexico border has put President Joe Biden in a difficult, politically threatening bind.
State and local Democratic leaders who should be among his closest allies heading into next year's presidential election are harshly criticising his handling of immigration. His probable 2024 Republican opponent, Donald Trump, is sharpening his attacks on an issue that has been a central part of his political message for almost a decade. And public support for Mr Biden on the situation is souring.
While voting is still more than a year away, the growing immigration crisis - whose effects are being felt thousands of miles from the US-Mexico border in part because Republican governors have been sending newly arrived migrants to Democratic-run cities - could be a daunting political drag on Mr Biden's popularity and his re-election hopes.
The numbers paint a darkening picture. According to preliminary US Department of Homeland Security figures obtained by BBC partner CBS News, US Border Patrol apprehended approximately 210,000 undocumented migrants entering the US during the month of September. That is the highest mark of the year, and comes close to matching the record peak monthly apprehensions of late 2022.
If the Biden administration thought the crisis at the border was easing and the national spotlight was moving to other issues after government policy changes earlier this year, the latest increase should dispel that notion.
What's more, the nature of the immigrant surge suggests there may be no end in sight. Roughly a quarter of the border apprehensions last month were citizens of Venezuela, the South American nation that has been struggling through political and economic hardship under the socialist dictatorship of Nicolas Maduro.
The Venezuelan exodus has created a hemispheric refugee crisis, with more than seven million fleeing the country - and the consequences are being increasingly felt on US soil.
More than 150,000 Venezuelans have headed north toward the US, across the Darian Gap into Central America, in the past two months, according to the government of Panama.
"People don't pick up and leave their homes just for the heck of it," Janet Napolitano, head of homeland security during the Obama administration, told the BBC. "They're usually in desperate straits - poverty, joblessness, high crime, violence, lack of civil institutions in their countries of origin."
Getty ImagesA US border guard observes migrants entering the USOn Thursday, the Biden administration announced two new steps to address the dramatic increase - and both have opened the president up to attacks from across the political spectrum. The president issued a series of environmental and planning waivers and released funds to build additional sections of wall along the US-Mexico border.
He also revealed that the US would resume direct deportations of Venezuelan citizens - a practice that had been suspended because of tense diplomatic relations between the two nations.
These new measures were quickly denounced as too little by immigration hard-liners and too much by left-wing immigration activists. The president's muddled explanations - that he still believes walls don't work and that it was money he was forced by Congress to spend - compounded the situation.
The Venezuelan announcement also represents a change in attitude by the administration, after moves last month to allow approximately half a million Venezuelan refugees in the US to apply for work permits and avoid deportation for 18 months.
In trying to assuage concerns that he is not doing enough to address the border surge while also keeping his liberal supporters happy, he appears to be satisfying no one - a conundrum that has played itself out repeatedly on border policy throughout the Biden presidency.
Immigration has become an intensely polarising issue, due in no small part to Mr Trump's "build the wall" rhetoric and sometimes draconian policies during his presidency. That has greatly curtailed Mr Biden's political flexibility in dealing with the crises.
Getty ImagesAn anti-immigration protest took place in New York last monthWhere Barack Obama was able to increase deportations and strengthen border security during his presidency without facing damaging blowback from liberal activists, Mr Biden has no such luxury. Every step he takes on immigration is now viewed in the context of the current environment of partisan political trench warfare, with Mr Trump and the Republicans on one side and the Democrats on the other.
Meanwhile, recent polling suggests that in that partisan fight, the public is turning on the president.
Respondents in a new Marquette University poll of registered voters were asked to choose who was "better" on the issue of immigration and border security, the current president or the man he replaced. Fifty-two percent said they preferred Mr Trump, while only 28% opted for Mr Biden.
That is tied with the economy for the largest issue gap between the two candidates and stands in contrast to topics like abortion and climate change, where Mr Biden has solid leads.
Those results were mirrored in an NBC News poll, which found 45% of Americans thought Republicans were better at dealing with immigration versus only 27% for Democrats. It represents a marked change from the Trump presidency, when pluralities of the US public preferred the Democrats.
Other presidents got money for a border barrier - why not Trump?The steady drumbeat of disturbing news from the border, as well as the strain on public services felt by the major US cities where the migrants are settling, is making a noticeable mark on public opinion.
And if the crisis does not ease before the 2024 general election campaign begins in earnest, the president will be taking on his Republican opponent on unfavourable political terrain.
According to Ms Napolitano, solving the immigration crisis will take a concerted effort from the Biden team.
"It requires diplomatic outreach," she says. "It requires investment in other countries so that we take away some of the incentive to migrate. And it requires strong border security and effective enforcement of our immigration laws, which need to be amended and reformed."
In the end, the criticism Mr Biden receives for his actions on immigration this week will be much less important than whether or not the new policies work. If they don't, and if the Biden administrations other steps to staunch the flow of migrants from Venezuela and elsewhere are also unsuccessful, his path to re-election becomes more perilous.
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