Migrant crossings at the US-Mexico border remain at their lowest levels since 2020, according to new federal data obtained by CNN, as Republicans and Democrats spar over border security.

Immigration remains among the top issues for voters and former President Donald Trump has made it a cornerstone of his campaign, pinning blame on Vice President Kamala Harris over the handling of the US-Mexico border and frequently turning to the issue on the campaign trail.

Harris’ visit to the US-Mexico border Friday was the clearest example yet of the campaign doubling down on border security by embracing strict rules that have been condemned by some corners of the Democratic party. The Democratic nominee tried to cast herself as the solutions-oriented candidate when addressing the US southern border, taking on a tougher stance while also pursuing broader immigration reform, in remarks Friday – an attempt at trying to close the gap with Trump on the issue.

But numbers have fallen drastically following executive action taken by the Biden administration over the summer.

In September, US Border Patrol recorded around 54,000 encounters along the US southern border, according to federal data – marking the third month of decline since the executive action went into effect.

It’s a notable shift from only months ago when Homeland Security officials wrestled with record numbers of border crossers and comes at a heated moment in the election cycle where border security has featured prominently.

Administration officials cite the executive action that President Joe Biden announced in June, which largely bars migrants from seeking asylum at the US southern border and levies harsh consequences on those illegally crossing, for the dramatic decline in crossings.

Migrants are still allowed to apply to legally migrate through other avenues, including a mobile app known as CBP One. US Customs and Border Protection processes 1,450 appointments daily.

“When you’ve seen previous things like this, they have been only enforcement at the border, and you have to have enforcement at the border, plus international collaboration, plus affirmative pathways for people to be able to come the right way,” a senior CBP official told CNN.

“And you have to do that all together, or else you’re just kind of putting a Band-Aid on an attempt to increase enforcement at the border. And it doesn’t work,” the official added.

The June measure can be turned on and off and lifted when there’s a daily average of fewer than 1,500 encounters between ports of entry, among other criteria. Daily encounters currently hover around 1,700.

But changes to that measure may make it harder for officials to lift it – a proposal that Harris floated while at the US southern border Friday, but campaign officials described it as different to what the administration has already been working on.

Asked about the timing of the change only weeks from Election Day, the senior CBP official said: “This is the natural next step in the rulemaking process.”

During her border trip, Harris described policies that would bar migrants from seeking asylum at the US southern border unless at a legal port of entry – marking a departure from decades-long protocol – and detailing harsh penalties for repeat border crossers.

“As president, I won’t only bring back the border security bill that Donald Trump tanked, I will do more to secure our border. To reduce illegal border crossings, I will take further action to keep the border closed between ports of entry,” she said. “We will pursue more severe criminal charges against repeat violators.”

“While we understand that many people are desperate to migrate to the United States, our system must be orderly and secure,” Harris added.