Gov. Mike Dunleavy of Alaska, a Republican, enacted one of the strictest measures on Monday when he ordered almost everyone arriving in Alaska, whether they live there or are visiting, to self-quarantine for 14 days and monitor themselves for symptoms of the virus. The state has 42 diagnosed cases — a smaller number of confirmed infections than in all but three other states — as of Wednesday afternoon.

“If you are a resident, your designated quarantine location is your residence,” the order said. “If you are a visitor or worker, your designated quarantine location is your hotel room or rented lodging.”

Historians said it was difficult to recall a time in modern American history when states imposed quarantine restrictions on residents of certain other states.

David M. Oshinsky, a medical historian, said he was not familiar with individual states taking such measures, but that during several polio epidemics in the 20th century, local officials forbade “outsiders” from entering their jurisdictions.

“In 1916, when newspapers blamed Italian immigrants in New York City for starting a serious polio outbreak, several surrounding municipalities used heavily armed policemen to patrol the roads and rail stations in search of fleeing New Yorkers and their children,” he said.

Other tensions — and some neighborly overtures — were rippling on state borders around the country as alarm over the virus continued to rise.

The $2 trillion stimulus package that was being debated by the Senate on Wednesday also had the potential to pit states against one another. Gov. Andrew M. Cuomo of New York, a Democrat, slammed it as “terrible” for the state, saying the $3.8 billion it would receive was “a drop in the bucket” given how hard New Yorkers had been hit by the virus.