Senior Trump administration officials have pushed American spy agencies to hunt for evidence to support an unsubstantiated theory that a government laboratory in Wuhan, China, was the origin of the outbreak, according to current and former American officials. The effort comes as Mr. Trump escalates a public campaign to blame China for the pandemic.

Some intelligence analysts are concerned that the pressure from administration officials will distort assessments about the virus and that they could be used as a political weapon in an intensifying battle with Beijing over the outbreak that has infected more than three million people across the globe.

Most intelligence agencies remain skeptical that conclusive evidence of a link to a lab can be found, and scientists who have studied the genetics of the coronavirus say that the overwhelming probability is that it leapt from animal to human in a nonlaboratory setting, as was the case with H.I.V., Ebola and SARS.

Reporting for The New York Times, Mark Mazzetti, Julian E. Barnes, Edward Wong and Adam Goldman investigate how scientists, spies and government officials have wrestled for months with varying theories about how the outbreak began. Many agree on the importance of determining the genesis of the pandemic. In government and academia, however, experts have ruled out the notion that it was concocted as a bioweapon. And they agree that the new pathogen began as a bat virus that evolved naturally, probably in another mammal, to become adept at infecting and killing humans.

A few veteran national security experts have pointed to a history of lab accidents infecting researchers to suggest it might have happened in this case, but many scientists have dismissed such theories.