Former US Secretary of State John Kerry has told the BBC his fellow Democrats allowed the US-Mexico border to be “under siege” during Joe Biden’s presidency.

In sometimes sharp words, Kerry – who was the Democratic presidential nominee in 2004 and a US senator from Massachusetts – said he told Biden the party had “missed” on the issue of immigration for years.

He said this had allowed Republicans like Donald Trump to gain political advantage.

The comments, made during an interview with BBC special correspondent James Naughtie, underscore an ongoing debate within his party over whether their pro-immigration policies cost them in recent elections.

Democrats have also wrestled with how they should handle Trump’s recent nationwide attempts to detain and deport undocumented migrants

“The first thing any president should say – or anybody in public life – is without a border protected, you don’t have a nation,” Kerry said. “I wish President Biden had been heard more often saying, I’m going to enforce the law.”

Such words have been a familiar refrain for Trump during his time in national politics and were included in the 2024 Republican Party policy platform.

But Democrats – many of whom advocate more relaxed immigration laws and a pathway to citizenship for undocumented migrants – attempted to portray Trump’s positions as harsh and discriminatory.

According to Kerry, that was a mistake.

“Trump was right,” Kerry said. “The problem is we all should have been right.”

In the first six months of Trump’s second term in office, illegal crossings at the US-Mexico border have dropped to near record lows – although the downward trend began during the last year of the Biden presidency, after the Democrat tightened some asylum rules.

The Trump administration has now shifted its focus to identification, detention and deportation of documented migrants across the US, expanding its efforts to include those who have resided in the US for years.

The move has prompted mass demonstrations in some US cities, including Los Angeles, where federal officials have been carrying out some of the most aggressive action.

Over the weekend, armed federal agents and 90 California National Guard troops conducted an operation in the city’s MacArthur Park – a gathering place for nearby immigrant communities. The officials swept through the park on foot, horseback and in armoured vehicles.

“To me, this is another example of the administration ratcheting up chaos by deploying what looked like a military operation in an American city,” Los Angeles Mayor Karen Bass, a Democrat, said at an impromptu news conference near the park.

“You can spin it anyway you like, but in my opinion, it’s a political agenda of provoking fear and terror.”

On Tuesday, Los Angeles and seven other California cities joined a lawsuit against the Trump administration, alleging that the federal immigration enforcement actions are unlawful. The state of California has filed a brief supporting the lawsuit.

Rob Bonta, the California attorney general, issued a statement denouncing what he said was a “cruel and familiar pattern of attacks on our immigrant communities by an administration that thrives on fear and division”.

The denunciations, and the legal battles, echo the tactics Democrats relied on during Trump’s first presidential term, when the Republican policy of separating migrant families that crossed the US-Mexico border generated widespread national outrage.

Such concerns faded, however, and by 2024 stringent immigration enforcement once again became a top Republican talking point.

The Trump administration appears to continue to welcome debate on immigration – an issue where, despite some declining support in recent public opinion polls, they believe they still have the upper hand.

When asked on Wednesday about a push by Democrats in Congress for legislation prohibiting immigration enforcement officers from concealing their identities, Trump said the opposition party had lost its way.

“This is the problem with the Democrats,” he said. “They have a lot of bad things going on in their heads. They’ve lost their confidence and become somewhat deranged.”

Democrats are used to derisive criticism from Trump, of course. But some – including party elders like Kerry – are becoming increasingly vocal in arguing that they given Trump an opening to land his political punches.

Reflections is on BBC Radio 4 on 10 July at 09:30 BST.

UK audiences can listen on BBC Sounds, or at this link for international users.