As the coronavirus gained a foothold in the United States, thousands of employees from Seattle to Silicon Valley were told to work from home. Public school districts in several states have shut down, universities are moving classes to online only, and even churches are limiting services or prayer meetings. A global health conference in Orlando, Fla., planned for Monday, which President Trump was supposed to address, will no longer happen.

Off the California coast, another cruise ship with infected passengers is waiting for a place to dock. The State Department on Sunday advised Americans, especially those with underlying health conditions, not to travel on cruise ships.

As the coronavirus spread to two-thirds of the states, Americans began to grasp the magnitude of the threat facing them. The weekend’s case tally ballooned, veering toward nearly 600 cases and close to 20 deaths.

In Washington State, with the epicenter in the Seattle area, Gov. Jay Inslee said on Sunday that he was considering mandatory measures to help keep people apart. Federal public health officials also signaled that the degree of community spread — new cases popping up with no known link to foreign travel — indicated that the virus was beyond so-called containment in some areas and that new, stricter measures should be considered.