Within the first 24 hours after Sen. Kamala Harris was named Joe Biden's running mate, top Democrats were reaching out to syndicated Black radio hosts, eager to line up appearances for Harris on their popular shows.

In roughly the same period, Biden's campaign cited Harris in a broad fundraising appeal, raising an impressive $34 million, largely from a new set of donors excited by Harris's role, and sold $1.2 million worth of Biden-Harris lawn signs.

And in coming weeks, the Biden campaign plans to deploy the U.S. senator from California to swing states — often virtually, but at times in person — to connect with Black voters, young activists and suburban women, groups whose support for Biden is solid but far from guaranteed. Joint television interviews are in the works over the next few weeks.

As the history-making running mate joined the Biden campaign in earnest Thursday — receiving a coronavirus briefing alongside him, issuing a joint statement on what are now called "Biden-Harris" policies, and meeting virtually with Biden's economic team — campaign aides said privately that they hope Harris can provide a jolt of charisma while giving Biden a sort of validation from a younger woman of color.

"That's what real leadership looks like," Harris said Thursday after the two emerged from a briefing and Biden called for a mandate that all Americans wear masks.

Thursday's event underlined that Biden and Harris will make attacking Trump on his handling of the pandemic central to their message. Biden has levied such criticism before, but Harris adds a new voice to the attacks.

Biden's advisers have delighted in Harris's rollout so far, even in how it has seemed to strike a nerve and prompted attacks, many of them unfounded and contradictory, from President Donald Trump and his allies.

"You have sort of a mad woman, I call her," Trump told Fox Business on Thursday morning. Later in the day, he baselessly questioned whether Harris was eligible to serve as vice president (as an American citizen born in Oakland, Calif., she meets all legal requirements).

The new alliance still felt fresh Thursday, with new staff, the unification of two political brands, and their families in a get-to-know-you phase. Harris met Biden for lunch at his house, where they were joined by Biden's sister, Valerie Biden Owens. Biden's sister is perhaps his closest and most important political adviser, playing the same role that Harris's sister, Maya, does for her.

But potential trouble spots also lurked as two very different individuals sought to come together.

One challenge is determining whether Harris's husband, Douglas Emhoff, will quit, or possibly take a leave of absence from, his job as a well-connected corporate and entertainment lawyer.

His firm, DLA Piper, touts him as representing "large domestic and international corporations and some of today's highest profile individuals and influencers in complex business, real estate and intellectual property litigation disputes." That is hardly a description calculated to endear him to the Democratic Party's resurgent left wing.

New presidential tickets typically barnstorm the country, testing their message and displaying what they hope will be evident chemistry before large crowds. Instead, Biden and Harris met for briefings on the novel coronavirus and the economy inside a ballroom at the Hotel Du Pont, an elegant and historic hotel in Wilmington, Del., where Biden announced his first Senate campaign in 1972.

Two wooden tables were set up in the room, with a giant video screen where health and economic advisers delivered their reports privately. Four doctors were on-screen when reporters were allowed in, along with charts labeled "Reported U.S. Coronavirus Cases" and "Percentage of Americans With Jobs."

Biden has said he has been getting such briefings almost every day, but Thursday was the first time Harris joined him.

Biden's top advisers say that Harris's presence on the ticket will not change the campaign's basic message but that she will deliver it in her own way. On Thursday, it was clear that the core of that message will be that Trump has bungled the biggest health crisis to face the country in a century.

Biden's campaign released a new 60-second ad highlighting his plans for the coronavirus, including increased testing, more child-care programs and nationwide standards and guidelines.

Biden also called on governors in all 50 states to require that every resident wear a mask outdoors, saying that would save the lives of at least 40,000 Americans.

"Every single American should be wearing a mask when they're outside for the next three months at a minimum," Biden said, pausing for emphasis on each word. "Every governor should mandate it."

Biden for months has talked about the importance of wearing face coverings, and he was mocked by Trump and his allies when he first appeared in public wearing a large black mask over his face. He said in June that, if he were president, he would do everything possible using his executive powers to require masks in public.

On Thursday, he described it as a civic responsibility akin to giving blood or donating food. Although masks can be uncomfortable, he said, they are key to getting life back to normal, including reopening schools and businesses.

"Be a patriot. Protect your fellow citizens," Biden said. "Step up. Do the right thing."

The message was intended as a contrast with Trump, who has often challenged the conclusions of public health officials and questioned their recommendations. Biden noted that the virus has killed more than 160,000 people in the United States and said Trump should have acted sooner and more aggressively.

"I hope the president has learned a lesson," Biden said, before reapplying his own mask.

Harris praised Biden and, reading from notes, articulated many of the policies that Biden has outlined over the past few months. They spoke less than eight minutes, however, and did not answer reporters' questions.

Earlier, Biden briefly answered a question about Trump's desire to cut Postal Service funding to prevent mail-in ballots.

"Pure Trump," Biden said, as one of his aides tried to usher reporters out of the room. "He doesn't want an election."

Trump later in the day rejected Biden's call for mandatory mask-wearing, suggesting his opponent's plans to combat the coronavirus would lead to increases in everything from suicides to heart disease to alcoholism.

He also accused Biden of "playing politics from the sidelines" and called the former vice president's plan "regressive," "anti-scientific" and "very defeatist."

The Biden campaign is hoping to carry the momentum from Harris's introduction into the Democratic convention next week. Biden and Harris are both planning to give their speeches from the Chase Center in Wilmington, rather than from Milwaukee, where the convention was originally planned.

Biden recently decided to stay in Delaware over concerns about the coronavirus. The waterfront events center, which has several ballrooms and an auditorium, is on a site that originally housed a shipbuilding facility during World War II.

Biden's campaign views Harris as a potentially strong voice in swing states — particularly around predominantly African American cities such as Detroit, Milwaukee, and Philadelphia —but also hope that she will motivate voters in immigrant-rich communities in Arizona, Florida, and Texas.

People close to Biden and Harris said the campaign is still deciding exactly how to deploy her but that just having her on television and at events with Biden will showcase a different face of the Democratic Party. One is a 77-year-old longtime Irish American pol, and the other is a 55-year-old first-term senator whose mother and father emigrated from India and Jamaica, respectively.