WASHINGTON — As John Hickenlooper, the former Colorado governor and current Democratic candidate for Senate, began another campaign event via Facebook Live last week, he stated the obvious to his virtual audience.

“The nature of campaigns has changed,” Mr. Hickenlooper said as he beamed his message out to the political world from his family room in a joint appearance with Kathleen Sebelius, the former Obama administration health and human services secretary who was back home in Kansas, to talk about coping with the novel coronavirus. “These times really are different, and we are going to be doing things differently on this campaign.”

Mr. Hickenlooper, who is hoping to oust Senator Cory Gardner, a Republican, is not the only one adjusting to a radically changed campaign reality. The sudden onslaught of coronavirus has upended the nation’s congressional races as many were just getting started, altering the political landscape in unpredictable ways and forcing candidates in the battle for the Senate and House to adapt to unique circumstances.

Campaign officials and strategists are trying to carefully game out the new reality. The crisis could prove to be a boost for incumbents who have a built-in advantage in providing services to constituents at a time when voters are on edge and in need. But it is also shining a potentially unflattering spotlight on Washington’s response to the pandemic, which could hurt lawmakers who were already facing an uphill climb to re-election.