LONDON — Boris Johnson is standing by his man — but it’s a political gamble that might yet cost him.

After lengthy face-to-face discussions with Dominic Cummings on Sunday afternoon, the British prime minister told the country he was confident that his chief adviser “acted responsibly and legally, and with integrity” despite alleged breaches of the U.K.’s coronavirus lockdown rules.

The revelation that Cummings traveled 260 miles from London to Durham to stay at a property close to family, after his wife developed coronavirus symptoms in late March, has led to calls for his resignation from opposition parties and a handful of Conservative MPs.

But Johnson, speaking at the government’s daily coronavirus press conference on Sunday evening, stood four-square behind Cummings — the strategic guru who masterminded the Brexit campaign and Johnson’s path to a thumping election victory.

The prime minister said he fully accepted the adviser’s explanation that he had “no alternative” but to travel to guarantee childcare for his four-year-old son should he and his wife become too ill.

Its a fault-line for Johnson’s government that the opposition Labour Party, under new leader Keir Starmer, is determined to exploit.

“I think he followed the instincts of every father and every parent,” Johnson said.

The U.K.’s guidance is that those who develop symptoms, as Cummings’ wife did, “must stay at home for at least seven days.” Other members of the household must stay put for 14 days.

But Johnson said the advice was also “absolutely clear that if you have childcare issues, that is a factor that has to be taken into account.” The official guidance advises parents who develop symptoms to “keep following” general advice “the best of your ability,” but acknowledges “not all these measures will be possible.” In short, discretion is limited.

Citizens who have made severe sacrifices and compromises in their own daily lives, though — including not being able to say goodbye in person to dying relatives — may feel that traveling hundreds of miles to stay near family stretches the parental allowances.

In truth, the precise interpretation of the rules now matters less than public perception — and initial polling looks bad for Cummings. According to a YouGov snap poll published Saturday evening, 68 percent of respondents said they thought Cummings had broken the lockdown rules, and several MPs reported having inboxes full of complaints from the public — many of whom have experienced similar situations to Cummings, but stayed put despite the difficulties.

Its a fault-line for Johnson’s government that the opposition Labour Party, under new leader Keir Starmer, is determined to exploit. “This was a test of the prime minister and he has failed it,” Starmer said. “It is an insult to sacrifices made by the British people that Boris Johnson has chosen to take no action against Dominic Cummings.”

Downing Street and senior ministers had rallied to Cummings’ defense on Saturday and the adviser himself insists that he acted “reasonably and legally” because he was acting in the interests of his four-year-old son.

But former Tory Immigration Minister Caroline Nokes tweeted on Sunday there could not be “wriggle room” for some people when it comes to lockdown restrictions, and that she had made her views clear to her whip.

Two days after the Guardian and Mirror first reported the story, it was still dominating front pages and the morning political shows on Sunday. These included new claims that Cummings had been spotted 30 miles from his parents’ house on Easter day and in Durham on April 19, allegedly on a separate trip up from London.

The latter was branded untrue by Cabinet minister Grant Shapps earlier on Sunday. When asked about the former, Johnson said he was “content that in all periods … he behaved responsibly and correctly,” although the prime minister pointedly avoided a specific denial.

But it is the first allegation that has lodged in the public memory — and Tory backbenchers are highly attuned to constituent anger over any suggestion that there is one rule for those in power and another for everyone else. In backing Cummings to the hilt, Johnson is risking a confrontation with his own MPs, many of whom have never been all that fond of Cummings’ radical, iconoclastic instincts.

“Cummings must go before he does any more harm,” prominent Brexiteer MP Steve Baker told Sky News’ Sophy Ridge on Sunday. “If he doesn’t resign, we’ll just keep burning through Boris’ political capital at a rate we can ill afford in the midst of this crisis.”

Other Conservative MPs have publicly joined Baker’s call, including Simon Hoare, Roger Gale, Craig Whittaker, Peter Bone and Damian Collins, with the latter saying Cummings has a “track record of believing that the rules don’t apply to him and treating the scrutiny that should come to anyone in a position of authority with contempt.”

The YouGov poll also found that 52 percent said they thought Cummings should resign. Meanwhile, an online petition calling for Cummings to be sacked had collected more than 140,000 signatures by Sunday evening.

Cummings is widely acknowledged, even by his critics, as a brilliant reader of public opinion. Under him, Johnson’s Downing Street has been assiduously monitoring and responding to what the public thinks.

Now, the question that decides how this saga ends could well be — what do they think of Cummings?

WASHINGTON — The United States will have a “better” vaccine than China — and it will have it sooner, former U.S. Food and Drug Administration Commissioner Scott Gottlieb predicted Sunday.

Data on the potential vaccines in clinical development in China “didn’t look overwhelmingly strong,” Gottlieb told Margaret Brennan on CBS’ “Face the Nation.”

“Those vaccines, if they do work, probably are going to provide lower levels of immunity than the platforms that the U.S. and Europeans are working with,” he said.

“So I think we’re going to have a better vaccine, and I think we’re probably going to have it sooner based on where we are in clinical development, some of the early progress that we’ve shown.”

Asked which potential U.S. vaccines are “most promising at this point,” Gottlieb cited one by the University of Oxford and AstraZeneca, as well as another by Moderna Therapeutics and Lonza.

Moderna’s showed promise in its first round of human trials earlier this month, fueling executives’ hopes that it could be ready in 2020.

“There’s a number of manufacturers that are either equidistant to them or not far behind,” Gottlieb said. “All look promising based on public statements they made and some of the preliminary evidence that they put out.”

President Donald Trump is pushing for a vaccine by the end of the year. Public health experts caution that while a vaccine that soon is possible, it is far from guaranteed.

“I would say that’s probably more likely a 2021 event that we’re going to have the vaccine available in sufficient quantities to mass inoculate the population,” Gottlieb said earlier this month.

David Cohen contributed to this report.