On Sunday, the senator announced he was placing himself under temporary quarantine in his Texas home. (Mr. Gosar did the same, followed by Mr. Collins and Mr. Gaetz on Monday. Mr. Gaetz, who was traveling with President Trump, learned after Air Force One lifted off from Orlando that he had been in touch with an infected person at CPAC. He then took a seat in an otherwise empty section of the plane.)

Mr. Cruz’s statement was detailed, measured and reassuring about his situation. “I’m not experiencing any symptoms,” he said, noting that “the medical authorities have advised me that the odds of transmission from the other individual to me were extremely low” and that those he’d interacted with since CPAC “should not be concerned.”

Mr. Cruz also stressed the need for vigilance. “Everyone should continue to treat this outbreak seriously and be driven by facts and medical science,” he said. He urged the public “to follow the recommendations of the C.D.C. and other health professionals.”

To the senator’s credit, he was focused on the coronavirus before it became personal. In January, he called on the administration “to issue a travel ban to and from China and implement advanced screenings at U.S. airports” — which may have struck many at the time as an overreaction. He has been outspoken about Americans’ need for “clarity” and “confidence in the government’s response.” Last week, he held a subcommittee hearing titled “From SARS to Coronavirus: Examining the Role of Global Aviation in Containing the Spread of Infectious Disease.”

This approach may strike many as unremarkable — the least a public official should do under the circumstances. But it stands in contrast to the dishonest, chaotic muddle that we’ve seen from the White House so far, as various officials send contradictory messages about a host of issues, including the scope of the problem, the availability of testing and the timeline for a vaccine. In his remarks at CPAC — as the virus circulated — Mick Mulvaney, then the acting White House chief of staff, blamed the news media for stoking panic because “they think this is going to be the thing that brings down the president.”