The demonstrations began before the convention got underway. But Denver authorities ran into their first major problems with demonstrators last night.
In the early evening the scene in and around a few blocks of Denver was growing more tense by the moment.
Hundreds of demonstrators appeared to be in a standoff with hundreds of police officers.
Most of the protestors looked young, probably in their early 20's. Some wore swimming goggles and makeshift gas masks fashioned from bandannas and other scraps of cloth.
Police officers clad in heavy black armor and sweating under their real gas masks stood in tight formation. They were armed with batons and other weapons.
In the end, officials say they arrested about 100 people for allegedly blocking the street, disobeying lawful orders and interference.
Secret Service agent Malcolm Weiley, a leader of Denver's Joint Information Center, said officials were not surprised by demonstrator tactics.
Just like their counterparts in the Twin Cities, Weiley says officials in Denver have been planning for months for how to handle scheduled, permitted demonstrations and other impromptu protests.
St. Paul Mayor Chris Coleman took a break from his Republican National Convention preparations in St. Paul to check in on the Democratic National Convention in Denver. Coleman declined to discuss what led to Monday's arrests, saying he didn't know enough about the situation. But Coleman did say he and others in Minnesota are closely watching how their counterparts in Denver are handling demonstrators.
"There's no question that we are learning from what they're doing, but every community has got to police in the way that reflects their community, so we'll do things you know a St. Paul way, in a Minnesota way when folks come to our town," said Coleman.
Denver resident Cynthia Kemper is originally from Minnesota. She and others in Denver had heard months of reporting about potential demonstrations. And when convention time came, Kemper was curious.
"I was one of those who said oh, let's go downtown," said Kemper.
Kemper took in the downtown scene on Sunday, the day the protests began.
She says Minnesotans are in for a surprise when they actually see what the police presence looks like on their streets, and she recommends checking it all out.
"I think it's real important for all of us to witness this first-hand and that not be afraid of it. But also it does give you the awareness of what does take place at these conventions and the forces that are tense with one and other, and so we need to be aware of that as citizens of a nation that believes in free speech and believes in keeping or that there's a balance between the two and so I think everyone should see it," said Kemper.
Mayor Coleman said efforts in St. Paul to keep the balance between order and protest will likely be somewhat different from Denver. But Coleman declined to offer any specifics.
"I think you'll just notice a difference in terms of how we're approaching it, in terms of how the officers are on the street and that. You know, I'd rather not go into great detail on how we're presenting, I just think you'll see a little bit different philosophy," said Coleman.
The RNC begins Monday in St. Paul. If the scene in Minnesota follows what happened in Colorado, demonstrations will begin breaking out in the Twin Cities this weekend.