In a briefing with reporters on Monday, Max Everett, the vice president of the Republican National Convention Committee, said organizers were “constantly looking at all sorts of different things we’ve got to look at, to make sure we have all our contingencies planned for well ahead of time.”

Major changes to the conventions could be a headache for both parties — for the Republicans, given Mr. Trump’s fondness for pageantry, and particularly for the Democrats, given the prospect that their party may need some unifying after a divisive primary.

Some infectious disease experts insisted that the most drastic scenarios were unlikely, and that canceling a convention would be a serious overreaction.

“I would recommend people travel, go ahead and go and have this thing,” said Dr. Herbert L. DuPont, the director of the Center for Infectious Diseases at the University of Texas School of Public Health, who believes a panicked response could be more disruptive than the virus itself.

Such anxiety, he added resignedly, has already “produced distrust of our government — and it’s going to affect, big time, this election.”

That is precisely what troubles those who watch election security closely. The coronavirus does not need to be severely damaging for the deep concerns about it to present risks that could be exploited by outside actors.

“The individual decision to go vote is much more vulnerable than the ballot itself,” said Yonatan Striem-Amit, a founder of Cybereason, a cybersecurity technology company. Presidential elections can hinge on small changes in turnout in certain areas, and turnout at that level could be easily manipulated in anxious times by someone running a misinformation campaign. A rumor spreading on social media about a local outbreak on Election Day, even if quickly proven to be false, could be enough to swing a precinct.