If a person insists on going, Fauci said, they should wear a mask, especially when they are yelling or chanting.
In an interview with ABC News' "Powerhouse Politics" podcast, Fauci said he understands the urge people have to participate in the political process but that the safest bet is to avoid congregating in large groups.
"It's a danger to the people who are trying to control the demonstration," he said of the recent protests over the death of George Floyd. "And it's a danger to the people who are demonstrating. So at the end of the day, it is a risky procedure."
When asked whether his advice also applies to Trump's plans to resume campaign rallies next week, Fauci said yes: "I am consistent. I stick by what I say."
The "best way that you can avoid -- either acquiring or transmitting infection -- is to avoid crowded places, to wear a mask whenever you're outside. And if you can do both, avoid the congregation of people and do the mask, that's great," he said.
"If you're going to be in a situation where beyond your control there's a lot of people around you, make sure you wear a mask," he said.
The president announced this week that he'll resume his signature campaign rallies beginning next Friday in Tulsa, Oklahoma. The state, which was among the earliest to begin loosening coronavirus restrictions, has a relatively low rate of infection but has seen cases rising.
ABC News contributed to this report.