(CNN) President Donald Trump wants America to know he's doing a great job in keeping out the novel coronavirus, in a victory lap that could look premature if his own experts are correct in their more somber forecasts.

The President spoke at a news conference on Wednesday about the worldwide health emergency that has seen the virus sweep into South Korea, Italy and every continent but Antarctica, sounding as if the danger had already passed rather than was yet to arrive.

"The risk to the American people remains very low," Trump said, as he unveiled his big announcement: Vice President Mike Pence will head the government effort.

The President's optimistic performance came hours before the Centers for Disease Control and Prevention said a patient in California who has the novel coronavirus might be the first person to be infected who did not travel to an afflicted region and was not exposed to another known carrier. The case raises the ominous possibility that the virus is already moving through the community.

In anxious times, including health emergencies, presidents are called upon to show authority and credible planning and to inspire confidence and national unity among Americans. The task is especially complicated for Trump, given the three years of divide-and-rule politics he has used to cement power, which has deepened mistrust among voters who do not support him.

His upbeat, election-year tone contrasted sharply with predictions from his government experts, who are warning of possible severe disruption to American life if the outbreak swells into a pandemic.

He enlisted some of those officials, who he touted as " tremendously talented ," in a rare appearance in the White House briefing room amid rising criticism that his administration's response to the virus is too little, too late.

Trump's main message was that there is nothing "inevitable" about a US outbreak. The President also claimed credit for his own wise steps that he said had kept Americans safe -- no thanks to Democrats, he said, who have branded his approach to a possible pandemic as small ball.

"We've done a great job in keeping it down to a minimum," the President said, crediting his early curbs on travel from China.

"Had I not made a decision very early on not to take people from a certain area, we wouldn't be talking this way. ... I took a lot of heat; some people called me racist."

His comments, taken literally, ought to have quelled any sense of panic. But the President's incessant political gamesmanship will make it difficult for many viewers to shed suspicion he was minimizing the situation for personal gain.

Presidents lead in fearful times

Trump's main aim Wednesday seemed to be to minimize the threat. He went out of his way to compare the novel coronavirus to the seasonal flu -- and marveled that so many Americans succumb to that ailment each year.

Presidents get judged on their handling of national crises. And Trump's appearance left many questions unanswered. Among them is whether he will be guided by science or politics in fighting the virus. Another is whether he has the capacity to rally the nation behind him if things take a turn for the worse. It's not a given that Trump has the self-discipline to manage the emergency and avoid counterproductive political grandstanding.

The President can be sure of staunch support from his base whatever happens, so any sense that a botched response could do for his presidency what the disastrous Hurricane Katrina relief effort did for George W. Bush may not materialize.

The imprecision of Trump's language Wednesday did not exactly inspire confidence, when he was asked if Americans should brace for a severe coronavirus outbreak.

"I don't think it is inevitable. I think we are doing a really good job. There is a chance it could get worse. There is a chance if could get fairly, substantially worse. Nothing is inevitable," the President said in a vague summary of scenarios.

He also preferred to focus on the cases of small numbers of Americans repatriated from Japan and China who developed the virus and are in quarantine, rather than the specter of a possible large-scale US epidemic that his officials fear.

"We're going to be pretty soon at only five people. We could be at just one or two people over the next short period of time," Trump said.

Yet health experts have said it is all but certain the coronavirus will end up being transmitted within the US given its rapid spread around Asia and Europe and across the world.

An awkward spot for health bureaucrats

Government health experts onstage with Trump had to tread a difficult line -- between honoring their professional assessments and avoiding angering the President, who dislikes being contradicted.

"Our aggressive containment strategy here in the United States has been working and is responsible for the low levels of cases that we have so far. However, we do expect more cases, and this is a good time to prepare," said Anne Schuchat, principal deputy director of the Centers for Disease Control and Prevention.

Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, delivered the sobering news that even with an unusually accelerated process of development and testing, it could be a year to a year-and-a-half before a vaccine becomes available. His assessment contrasts with Trump's hints that inoculations are just around the corner.

As is often the case in Trump's presidency, nonpartisan career officials were forced to stand by his side as he unleashed flaming attacks on political opponents -- in this case House Speaker Nancy Pelosi, who had suggested to CNN earlier that he did not know what he was talking about on the coronavirus.

"I think Speaker Pelosi is incompetent. ... She is trying to create a panic and there's no reason to panic because we have done so good," Trump said, with Schuchat -- wearing a neutral expression -- beside him in the camera shot.

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A dividing line in tone and professionalism became clear between the politicians, who took time out for obligatory praise of Trump, and the professionals.

"The President's early and decisive actions, including travel restrictions, have succeeded in buying us incredibly valuable time," Health and Human Services Secretary Alex Azar said.

Pence, whose new responsibility might turn into a poisoned political chalice if the outbreak reaches America and exacts a heavy toll, also lauded Trump.

"From the first word of an outbreak of the coronavirus, the President took unprecedented steps to protect the American people from the spread of this disease," he said.

Confusion about the exact division of responsibilities between Pence and Azar suggests a not entirely smooth plan.

"I'm still chairman of the task force," Azar said, adding, "I was delighted that I'd get to have the vice president helping me. Delighted."

Such a hierarchy did not seem to be what the President had in mind when he said, "I'm going to be putting our Vice President Mike Pence in charge ... he's got a certain talent for this."