Former President Donald Trump said amid a campaign shake-up Thursday that Vice President Kamala Harris is a proven failure on economic issues and, if she is elected this fall, the “worst is yet to come.”

Mr. Trump said the “big facts” and “substantial truths” show Ms. Harris “broke the economy” by backing wrongheaded policies that fueled inflation.

“She destroys everything she touches, and if she wins, your finances and your country will never recover,” Mr. Trump said, standing in front of a table displaying boxes of cereal, coffee, and fruits at Trump National Golf Club in Bedminster, New Jersey. “You don’t have to imagine what a Kamala Harris presidency would be because you are living through that nightmare right now.”

---

---

Mr. Trump also confirmed reports that 2016 campaign manager Corey Lewandowski was joining his campaign. Mr. Lewandowski popularized the “Let Trump be Trump” mantra. However, Mr. Lewandowski left during the campaign eight years ago amid turmoil, including when he shoved a journalist on camera.

Mr. Trump said Mr. Lewandowski would serve as a “personal envoy” and dismissed reports he was considering firing senior advisers Chris LaCivita and Susie Wiles. The campaign has been on the defensive as Ms. Harris has gained ground in polls.

The press conference marked the second time in as many days that Mr. Trump tied Ms. Harris to President Biden on the campaign trail and took particular pains to attack her economic record.

The refocused message and Mr. Lewandowski’s return are part of a campaign reset that comes weeks after Mr. Biden pulled out of the race and endorsed Ms. Harris.

Mr. Biden’s exit came after numerous polls showed he was losing to Mr. Trump in most of the battleground states. Voters had concerns about his age and disapproved of his handling of various issues, including the economy and immigration.

The horserace has changed since the switch atop the Democratic ticket.

Ms. Harris’ pending nomination has energized party activists. Polls show she has eaten into or erased Mr. Trump’s lead.

Ms. Harris is set to formally accept the nomination next week during Democratic National Convention in Chicago.

Meanwhile, Mr. Trump has started to focus more on drawing a contrast with Ms. Harris on the issues and steering clear of the personal attacks that could scare away some voters.

“I don’t think people know who she is yet,” Mr. Trump told reporters. “People don’t know who she is. She is a radical left socialist.”

On Friday, Ms. Harris plans to propose the first-ever federal ban on “corporate price-gouging in the food and grocery industries” to reduce consumer prices.

Mr. Trump said Ms. Harris’ economic vision includes “price controls” that will lead to more financial hardship, raising taxes on income and capital gains taxes, abolishing private health care, and closing power plants.

Mr. Trump scoffed at the idea that Ms. Harris would prioritize the economy on Day One in office.

“Day One, really for Kamala, was really three-and-a-half years ago,” Mr. Trump said. “Where has she been and why hasn’t it been done?”