Just as the Joe Biden campaign team is on a roll, and in great shape according to the polls, they've hit an obstacle.
The vice-presidential candidate, Senator Kamala Harris, has been forced to abandon her schedule with fears that she may have contracted Covid.
There's no evidence she has the virus, but two people with whom she has been in close contact have just tested positive.
Her communications director, Liz Allen, and a crew member on a recent flight are both infected, so out of an abundance of caution Senator Harris is being pulled off the campaign trail.
But this shouldn't change the central dynamic of the race that is all trending towards the Democrats.
If you are Joe Biden right now, you want to do as little as possible that might change the headlines.
His strategy is clear: Create no noise, offend no voter group, take no risk.
Above all, don't get Covid.
The Democratic presidential candidate is in great shape going into the final 19 days of the campaign.
Polling shows him with a commanding lead both nationally and in many of the battleground states.
Biden is highly competitive where he shouldn't be - Texas, Iowa, Georgia.
He's way out in front where he would expect to be in a dog-fight - Wisconsin, Pennsylvania, Arizona
There are a few states where the polling is more erratic and the race hasn't settled - Minnesota, Florida, Ohio - but there is no question that Donald Trump is facing a potential rout on November 3.
That doesn't mean he or his supporters will accept a loss.
In Florida earlier this week I spoke to two supporters, Tracy and Lou Comtois, who spoke for many of his loyalists.
They do not believe the polls at all.
And if Trump loses, they believe it will be because of election fraud.
The problem for the Republicans is that their attempt to portray Biden as a far-left candidate has largely failed.
You can say many things about the 77-year-old former VP, but he's just not a radical.
Few Americans regard him a threat.
Ineffective, too old, past his peak, wrong on important issues. Perhaps. But a socialist? Or a hostage to extremists?
Biden is not Hillary Clinton. He doesn't have her negative ratings; he doesn't antagonise a subset of voters like she did.
And that means that he may be unstoppable.