At Tuesday's raucous rally in Atlanta, Vice President Kamala Harris went after former President Donald Trump on what polls show is his strongest campaign issue: immigration.

“In this campaign, I will proudly put my record up against his any day of the week,” Harris said, “including on the issue of immigration.”

Harris told her audience that Trump “does not walk the walk” when it comes to border security, noting that he instructed Senate Republicans to vote against a bipartisan Senate bill intended to curb illegal crossings along the U.S.-Mexico border.

“Our administration worked on the most significant border bill in decades,” Harris said. “Some of the most conservative Republicans in Washington, DC, supported the bill. Even the border patrol endorsed it. It was all set to pass, but at the last minute, Trump directed his allies in the Senate to vote it down. He tanked the bipartisan deal because he thought it would help him win an election.”

The bill in question

In late 2023, the Biden administration faced Republican opposition in Congress to continue funding Ukraine in its war against Russia. GOP lawmakers demanded that the president sign on to border security measures in exchange for agreeing to send more money and weaponry to Kyiv. Biden agreed, and a bipartisan bill was hashed out.

Dubbed the Emergency National Security Supplemental Appropriations Act, the legislation proposed the construction of new border barriers, an expansion of detention facilities and the hiring of more border patrol agents and immigration judges. It also proposed ending the “catch and release” policy for those applying for asylum from other countries, and would have given more money to try to stop the flow of fentanyl and human trafficking into the U.S.

While few Republicans described the legislation as perfect, the bill had enough support to pass — until Trump pressured his party to reject it.

“Only a fool, or a Radical Left Democrat, would vote for this horrendous Border Bill, which only gives Shutdown Authority after 5000 Encounters a day, when we already have the right to CLOSE THE BORDER NOW, which must be done,” Trump wrote on Truth Social of the legislation on Feb. 5.

The surge in immigration and its polling impact

During the Biden administration, roughly 7 million migrants have been arrested for illegally crossing the U.S. southern border, government data shows, a figure that does not include so called “go- aways,” those who cross the border but evade arrest.

With the annual number of illegal border crossings averaging 2 million in 2021 and 2023, Biden, who also increased the number of deportations from the U.S., implemented a series of measures in early 2024 that have curbed that number. Still, 1.3 million migrants crossed the Southern border in the first 9 months of the fiscal year 2024.

Ten days before Biden withdrew from the 2024 presidential race on July 21, the Pew Research Center released a poll showing that on immigration policy, Americans preferred Trump to Biden by a margin of 52%-35%. A YouGov poll released the day after Biden announced his exit found that Harris trailed Trump on the issue of immigration by 15 points (45%-30%).

Trump and his Republican allies go on the attack

Over the last week, Trump has released multiple campaign ads that attack Harris on immigration, two which falsely assert that Biden named her his “border czar.”

“Joe Biden made Kamala Harris border czar to fix immigration,” one ad states.

In fact, with illegal immigration spiking early in his presidency, Biden tasked Harris in March 2021 with heading up his administration's efforts to address the "root causes" of migration from Central America.

“I’ve asked her, the VP, today — because she’s the most qualified person to do it — to lead our efforts with Mexico and the Northern Triangle and the countries that help — are going to need help in stemming the movement of so many folks, stemming the migration to our southern border,” Biden said.

In that role, Harris convinced some companies to open businesses in countries like El Salvador, Guatemala and Honduras, expanding job opportunities, but her efforts did little to stem the flow of migrants to the U.S.

As a result of her high profile assignment and the continued surge of illegal immigration, Harris was put in a vulnerable political position, and Republicans have repeatedly gone after her on it.

"And let me remind you. Kamala had one job. One job. And that was to fix the border. Now imagine her in charge of the entire country," former South Carolina Gov. Nikki Haley said during her speech at the Republican National Convention prior to Biden’s exit from the race. .

Turnabout is fair play

With Republican attacks on Harris on the issue of immigration sure to play a central role in the last three months of the 2024 campaign, the vice president is hoping to flip the script on Trump, highlighting her time as “attorney general of a border state,” as she said at Tuesday’s rally in Atlanta.

“In that job, I walked underground tunnels between the United States of America and Mexico on that border with law enforcement officers,” she said. “I went after trans-national gangs, drug cartels and human traffickers that came into our country illegally. I prosecuted them in case after case, and I won.”

Whether that reasoning will put a dent in her polling numbers on immigration, however, remains to be seen.