Vice President Kamala Harris worked to turn the tables on border security, Donald Trump’s strongest issue against her in the coming presidential election, promising Friday to take a harder line on those who cross the border illegally and accusing the former president of deliberately sabotaging legislation that would have helped solve the problem.

“It was the strongest border security bill that we have seen in decades. And it should be in effect today,” the Democratic presidential nominee said in a 24-minute speech near a port of entry in southern Arizona. “But Donald Trump tanked it…. He prefers to run on a problem instead of fixing a problem.”

Harris said she would continue President Joe Biden’s new policy that has dramatically cut illegal border crossings by ending asylum requests for those who did not come into the country at an authorized port of entry once such crossings exceeded 2,500 per day over seven straight days. And she said she would increase criminal penalties on repeat offenders.

“I believe we have a duty to set rules at our border and to enforce them,” she said.

Harris was introduced by a mother who lost a son to a fentanyl overdose, and she spent several minutes discussing the “scourge” of that drug’s effects on Americans. She reminded her audience that as a two-term attorney general of California, she prosecuted Mexican smuggling gangs.

“I walked through tunnels that traffickers used to smuggle contraband into the United States,” she said. “I’ve seen tunnels with walls as smooth as the walls of our living room, complete with lighting and air conditioning, making very clear that it is about an enterprise that is making a whole lot of money in the trafficking of guns, drugs and human beings.”

Harris also criticized Trump for making no effort to reform the immigration system during his four years in office, and she said she would make that a priority, particularly to offer a path to citizenship for those who were brought into the country illegally as children.

Biden, before he ended his reelection campaign, had been polling far behind Trump on the issue of illegal immigration, but Harris has managed to close that gap somewhat in recent polls. She has aggressively blamed Trump for scuttling the measure that would have added 1,500 more Border Patrol agents and paid for 100 new machines to detect fentanyl at ports of entry, which is where the vast majority of it has been coming into the country.

That Trump persuaded his GOP allies to stop the legislation early this year is not in dispute.

Sen. James Lankford of Oklahoma, the lead negotiator for Republicans on the bill, supported it, saying his party was getting much of what they wanted on border security. He told Fox News that Trump personally lobbied his colleagues to kill the bill in an effort to help his campaign to regain the White House.

“Trump said don’t fix anything during the presidential election. It’s the single biggest issue, don’t resolve this. We’ll resolve it next year,” Lankford said.

And Trump himself acknowledged at the time that he did not want the bill to pass. “Please blame it on me. Please,” he said at a Jan. 27 rally.

Since Harris became the presumptive Democratic nominee after Biden dropped out in July, Trump has accused her of failing to solve the illegal immigration problem despite being “the border czar.”

“She’s done the worst job, probably in the history of any border, not just our border,” he said in remarks to reporters Thursday in an attempt to rebut Harris’ Arizona visit in advance.

Harris has correctly noted, though, that her brief was to find and address the root causes of migration flows from Latin America into the United States, not to “secure” the border.

Harris has proved since becoming Trump’s opponent to be a more effective communicator than Biden. In her Sept. 10 presidential debate with Trump, for example, she answered an immigration question by making it entirely about Trump, accusing him of blocking the border bill solely to keep it alive as a campaign issue.

She then tangentially noted that Trump’s rally-goers leave his events before he has finished speaking, which then drew from him an angry response that devolved into his now infamous lies that Haitian immigrants were eating their neighbors’ pets in Ohio.

The coup-attempting former president, who is now also a convicted criminal awaiting sentencing, made illegal immigration a cornerstone of his 2016 presidential campaign and repeatedly promised he would force Mexico to pay for a massive border wall of reinforced concrete.

Upon election, however, Trump made no effort to get Mexico to pay and ultimately raided money earmarked for housing and schools for military service members and their families to build his promised wall, which by then had morphed into a slightly taller version of the steel border fence that been started by President George W. Bush and continued under President Barack Obama.

By the time Trump left office, there were only 52 new miles of fence built where there previously had been no barrier along the 1,954-mile border. An additional 400 miles of 18-to-30-foot steel fence was constructed to replace older fencing.