WASHINGTON — The oldest Republican in the Senate tested positive for it. The oldest member of the House was hospitalized with it. And several more lawmakers have announced they have either been diagnosed with the coronavirus or are quarantining after exposure to it, in what is threatening to become a minioutbreak on Capitol Hill that has already disrupted the business of Congress.

Sen. Charles E. Grassley, R-Iowa, 87, on Tuesday became the latest lawmaker to be affected, announcing that he had tested positive. His absence helped to temporarily derail the confirmation of President Donald Trump’s nominee for the Federal Reserve Board and shattered Grassley’s pride and joy, the longest consecutive voting streak in Senate history.

His diagnosis came the day after Rep. Don Young, R-Alaska, also 87, disclosed that he had been hospitalized over the weekend after what he described as a particularly brutal bout with COVID-19. The twin announcements from two men whose gender and age put them at peak vulnerability to being killed by the virus underscored the risks that lawmakers are operating under as Congress continues to meet.

The marble-and-stone petri dish that is Capitol Hill is a vivid microcosm of the national struggle to confront and contain the spread of the pandemic, with partisan bickering often thwarting already unevenly enforced health precautions. Having effectively declared themselves essential workers, the nation’s lawmakers — a group of older Americans whose jobs involve weekly flights, ample indoor contact and near-constant congregating in close quarters — are yet again struggling to adapt their legislative and ceremonial routines to stem the spread of the virus, even as it rages within their ranks.

As of Tuesday afternoon, both Sen. Rick Scott, R-Fla., and Grassley were in quarantine as a result of possible exposure, marking the first time Grassley had missed a vote since 1993. In the House, Young — who noted on Monday that he was “alive, feeling better and on the road to recovery” after being discharged — is among four lawmakers who have revealed they contracted the virus in the past month.