Joe Biden is accusing President Trump of failing to act decisively to protect the nation’s economy from the coronavirus pandemic and allowing corruption to seep into the $2 trillion stimulus package.

Mr. Biden on Monday began airing a digital ad in six battleground states that offers a timeline of the pandemic’s spread, saying the president “didn’t build a great economy. His failure to lead destroyed one.”

Mr. Biden’s campaign told The Wall Street Journal that if elected, the former vice president would appoint an inspector general on his first day in office to conduct a retrospective, top-to-bottom review for potential malfeasance of every stimulus loan provided under the CARES Act.

“Any dollar that goes to someone who does not merit it under the law, any dollar taken corruptly, we will find it, we will come get it and we will punish the wrongdoers,” Mr. Biden said in a video released Monday.

Erin Perrine, a spokeswoman for the president’s re-election campaign, called the ad “another absurd and factually inaccurate attempt to be relevant” by Mr. Biden. She said “tens of millions of jobs and businesses in America were protected by President Trump’s work to establish and fund the Paycheck Protection Program.”

Mr. Biden, the likely Democratic presidential nominee, has seized on the president’s response to the outbreak and expressed doubt over the administration’s commitment to ensuring that stimulus funds reach struggling workers and small businesses.

Mr. Biden said in an interview Tuesday with ABC’s “Good Morning America,” that the president has been “incompetent” in his handling of the virus.

The former vice president said his political standing had not been hurt by being forced to remain at his Delaware home. “We're winning if you look at all the polling data,” he said.

The digital ad will appear on Facebook, YouTube and Instagram in Arizona, Florida, Michigan, North Carolina, Pennsylvania, and Wisconsin. Mr. Biden said Monday night at a fundraiser that he was preparing “a detailed plan for the right kind of economic recovery.”

As vice president, Mr. Biden oversaw the nearly $800 billion economic recovery in 2009 and has made the Covid-19 stimulus a central message against Mr. Trump, saying the funds have helped politically connected allies of the president at the expense of small business.

Mr. Biden and Democrats have also pressed for greater oversight, railing against Mr. Trump’s decision to sideline the Pentagon’s acting inspector general, Glenn Fine, who had been set to oversee the new Pandemic Response Accountability Committee.

In the video Mr. Biden said he would empower his inspector general to refer any potential criminal activity to the Justice Department, calling his plan a warning “to anyone who participates in the corrupt giveaways of President Trump and his administration.”

Last week, the White House lawyer tapped to oversee a part of the broader CARES Act said he would act independently from the Trump administration.

Brian D. Miller was nominated by the president to serve as special inspector general for the coronavirus pandemic recovery, or SIGPR, with responsibility for monitoring the Treasury Department’s use of $500 billion to help businesses.