As cases rise exponentially across the United States, the novel coronavirus is quickly looking to be one of the toughest challenges facing the United States in years. But David Gergen — who served as an advisor to Presidents Reagan, Nixon, Ford and Clinton — says that President Trump, unlike many of his predecessors has not risen to the challenge of the times.

“It’s clear he has not found his voice to rally the country in the way that, say, Ronald Reagan did or George W. Bush did. He hasn’t united us,” said Gergen, who joined Jim Braude on WGBH News’ Greater Boston via Skype, along with his daughter, Dr. Katherine Gergen Barnett, a physician at Boston Medical Center who has witnessed the pandemic from the front lines.

“[Trump] did a good thing early on, and he deserves more credit, for slamming the door shut on Chinese coming in,” Gergen said, referring to Trump’s controversial order to restrict travel from China, where the virus first took hold.

“[But] since then there has been a lot of bumbling and a lot of delays that have been hard to explain,” he added.

Dr. Katherine Gergen Barnett said, in particular, delays in testing are making it harder for hospitals to keep both patients and doctors safe.

“We are really struggling very hard against a ticking clock, which is that we do not have adequate tests available for the hundreds of people who are concerned, who may have symptoms … and yet do not yet fit the parameters for testing,” she said.

Without the tests, she explained, it is much harder for doctors to “figure out who’s sick and who’s not sick and who can stay in the hospital and who can go recuperate at home.”

The elder Gergen, who is now a professor at Harvard University’s John F. Kennedy School of Government, said that the president’s efforts to blame the pandemic on China, by repeatedly calling it the “Chinese virus,” will make it harder to get control of the outbreak.

“He engages in shifting blame on a regular basis and he’s now made the Chinese a scapegoat and … in China, they’re calling this the American disease. It doesn’t help the people on either side,” he said. “We ought to be in highly cooperative relationships with countries around the world to see if we can end this crisis.”

Dr. Gergen Barnett, who serves as the vice chair of primary care innovation and transformation and the program director of the department of family medicine at Boston Medical Center, says she takes comfort in the cooperative relationships she has seen on the state level.

“People need to think outside the box and come together with a greater mission and vision,” she said. “Being part of multiple conversations with leaders around the country and really leaning into colleagues who are in places like Washington state, which has been hardest hit, to say ‘what’s working for you’ … has been really heartening.”