This is not just a USA only problem. This turn of events affects other countries in a negative way, amirite?
I think the main concern is the spread of covid-19 here. Judging by the number of people involved in close quarters, this would have to be a super-spreading event.
"As few as 10 percent of infected people may drive a whopping 80 percent of cases in specific types of situations" By Christie Aschwanden on June 23, 2020 scientificamerican
"it was estimated that between 10-20% of those infected are responsible for 80% of new cases. The new models confirm that basic picture, with most cases coming from relatively few superspreader events (if you count all the subsequent people infected by those who were infected at a superspreader event)." Steven Novella on November 4, 2020
"At churches, on cruise ships and even in the White House, superspreading events that can sicken dozens, even hundreds, of people have illustrated the potential for the coronavirus to infect in dramatic bursts.
Experts say these large clusters are more than just extreme outliers, but rather the pandemic's likely main engine of transmission." Kelly MACNAMARA
November 19, 2020
The point is super spreading events are the main driver. Most people get infected via super spreading event, not touching a grocery cart handle with covid-19 and then touching their face.
Now, this is bad enough since pandemics don't respect nation's borders. Even New Zealand is having trouble with quarantine breaches. Meaning a certain percantage of the infected at U.S. capital super-spreading effect will spread the infection to other countries.
Even worse is mutations. The more people infected the more mutations, the more variants and possibly strains of virus.
"his variant seems to spread more easily and quickly than other variants. " CDC Updated Jan. 7, 2021
That means more covid-19, more mutations, and possibly a new variant for the rest of the world. Even if this doesn't result in a new variant, mutations are cumulative. So it might only get 50% of the mutations required to be a new variant, but that's 50% closer.
The actions of the rioters were highly irresponsible and will have consequences that will effect many countries.
I'm not sure if there was any threat to other countries other than the spread and mutation of covid-19 from the event. Some might say it was an attack on Democracy, but it was unsuccessful attack because Biden was confirmed by Congress anyways.