Donald Trump on Wednesday used various adjectives to contend his administration responded swiftly to the coronavirus amid a wave of criticisms from Democrats about a snail-like federal effort.

The president, who will tour US Centers for Disease Control and Prevention (CDC) headquarters in Atlanta on Friday after visiting tornado-ravaged Tennessee, told a group of Latino officials in town for a conference, that the United States is better prepared to counter a threat or crisis than any other country.

He used words like "quickest" and "aggressive" and "raced" to describe how he and his team moved to counter the mysterious virus, for which there is no vaccine or treatment drugs. (The Trump administration and drug industry have begun work, but his own officials have reminded the president daily that testing will take a year.)

Mr Trump touted his government's response as the "quickest and most aggressive response in modern history," contending he "marshalled American industry and science."

And when it came time to start work on a possible vaccine, he claimed his team "raced" to get that complicated and time-consuming work started.

But Democratic lawmakers and some of that party's current and former presidential candidates have said the administration's response was anything but the "quickest" and "most aggressive."

To be sure, Mr Trump's management of the growing crisis –– there are now 108 cases on US soil, with 11 deaths – likely will be a campaign-trail issue until Election Day.

The Democratic race, after former Vice President Joe Biden's Super Tuesday comeback that saw him officially pick up a 10th win in Maine on Wednesday, is now a two-candidate race between Mr Biden and Vermont Senator Bernie Sanders.

"Let the experts take this over," Mr Biden told CNN on Friday. "Everyone will have more confidence."

The former VP blamed a recent stock market slide "not just the pandemic concern, but the way in which the president is handling this."

Mr Sanders also has panned the president's handling of the health scare.

"You would think that you'd have a president of the United States leading, working with scientists all over the world, bringing people together to figure out how we're gonna deal with this crisis. He is here in South Carolina," Mr Sanders said the same day, criticising the president for going ahead with a South Carolina primary eve campaign rally in North Charleston rather than focusing on the virus outbreak response.

Mr Trump, however, has been involved in the response.

He toured the National Institutes of Health on Tuesday and has been meeting with government and industry experts daily. He told reporters earlier this week he is devoting quite a bit of his working days to virus efforts.

But he also has tried to downplay the risk, with he and Mr Pence sounding a steady drumbeat that the overall risk to Americans is "low."

And the president has had some fun with the situation, sounding flippant on Tuesday when he observed the virus has the entire world "aflutter." Then came this quip on Wednesday during a White House meeting with airline executives about keeping travellers virus-free: "I haven't touched my face in weeks! I miss it."