People around the world have also planned their own protest against the United States president.
Organizers for the "March for Truth" rallies Saturday say their objective is to "let our elected leaders know that Americans want answers".
"We gotta keep up the fight, that's all there is to it", said Jon Lovett, a former President Barack Obama speechwriter and popular podcast host, who spoke at the D.C. rally.
The chants at the D.C. march were clever and cumbersome, taking wonky and specific aim at what the protesters believe have been White House attempts to cover up its connections with the Russian government.More news: Spieth right back in the mix at Memorial
Comey, who had been leading an investigation into alleged ties between the Trump presidential campaign and Russian Federation, was sacked earlier last month.
That rally was dubbed "Pittsburgh, Not Paris" - a reference to the president's statement Thursday, in announcing his plan to withdraw from the global climate treaty, that "I was elected to represent the citizens of Pittsburgh, not Paris".
Trump announced Thursday his decision to pull out of the global climate agreement, joining Syria and Nicaragua as the only countries that are not part of the Paris agreement. A few hundred protesters also demonstrated against Trump near one of his New Jersey golf clubs.
Only a day after he took office on January 20, millions of people pour to the streets in cities around the world for the Women's March. "We will not go back to sleep".More news: Trump not planning to invoke executive privilege to block Comey testimony
In what some saw as a nod to his campaign promise to revitalize the country's coal industry, Trump also said, "It is time to put Youngstown, Ohio; Detroit, Michigan and Pittsburg, Pennsylvania, along with many, many other locations within our great country before Paris".
The Trump supporters included Vince Harrison, 56, a burly retired firefighter from Washington, who said it was his first rally ever.
"The fact that this man could be president for four years scares me to death", he said.More news: California, Other States Vow to Lead as Trump Exits Climate Pact
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