There were an estimated 5,000 people in that crowd in Denver, gathered to hear socialist Sen. Bernie Sanders speak. And speak he did. This from the Denver Post:

Breathing a progressive political fire, Vermont Sen. Bernie Sanders ignited Colorado supporters with a blistering condemnation of billionaires and corporations, drawing a crowd of nearly 5,000 to Denver — the largest of his Democratic presidential campaign since the May kickoff.

And as the story notes, while this crowd was the largest for Sanders since he began running for president last month, it's far from the only big crowd he has drawn.  More than 3,000 people were at a Sanders event in Minneapolis at the end of May. Earlier this month, more than 700 people were at a Sanders rally at Drake University in Iowa. In early June, an overflow crowd turned out to hear Sanders in Keene, New Hampshire.

Sanders, himself, has been taken aback by the size of the crowds coming to see him. "If you were to ask me a couple of months ago whether we would have larger crowds than any other candidate out there, I would not have told you that that would be the case," he told NPR.

The question now is what (and how much) the packed houses Sanders is playing to actually mean.

Here's what we know for sure: That Sanders -- and the populist, anti-big business message he is championing -- is driving more excitement in the Democratic base than I certainly thought it would.  While polling suggested that there was a growing bloc of liberals who wanted a liberal candidate to fully embrace their agenda, that the rallying behind Sanders among that group has happened so quickly is surprising.

We also know that crowd size is one -- if far from the only -- indicator of organic energy in politics. If 700 people are willing to come see Sanders speak in June 2015 in Iowa, it's not that hard to imagine some decent portion of those people will also be willing to turn out and caucus for Sanders come Feb. 1, 2016.

Crowd size also can function as a leading indicator of a growing movement -- a sort of early-warning system that something is brewing out in the country that hasn't made its way to the political class back in Washington, D.C. I remember vividly during the 2006 election cycle when a freshman Senator named Barack Obama was the most sought-after surrogate for Democratic candidates in tough races. And how everywhere he went -- even in conservative-minded states like West Virginia -- thousands of people showed up to catch a glimpse of him.

Not everyone knew it then -- and Hillary Clinton was one of the unknowing -- but the energy around Obama in 2006 was a precursor to a movement that swamped the former first lady and overwhelmed John McCain in 2008.

So, is Bernie Sanders the second coming of that sort of movement?

Here's what gives me pause on drawing that conclusion: Aside from Obama, the candidate in recent years most able to generate genuine and organic enthusiasm (as well as big crowds) was former Texas representative Ron Paul. I still remember vividly how the Paul forces overwhelmed virtually every Republican candidate forum and debate in which he appeared.  Walking around the Ames Straw Poll (R.I.P.) in August 2007, I was convinced that Paul had a chance to shock the world (okay, the political world) with a stronger-than-expected finish. He finished fifth. And he went on to never win a primary or a caucus in either his 2008 and 2012 presidential candidacies.

For Paul, the crowds he generated were misleading. Yes, every single person who turned out for him was willing to do anything to see him elected. The problem? The people who showed up were almost all of the people that were for Paul.  As in, the energy and excitement he generated was real but it wasn't nearly widespread enough to elect him or even come close to electing him.

Think of it this way: Paul was the most popular band in your high school. EVERYONE loved them and thought they were going to be the biggest thing ever. Everyone in your high school.  Not everyone in the world. Obama in 2006, on the other hand, was like seeing the Beatles at the Cavern Club in 1961. There was something coming, something big, and though you might not have been able to grasp then how big it was going to be, you knew you were there at the beginning of something. (Note for haters: I am not saying Obama is the Beatles. I am simply using a metaphor.)

So, is Sanders 2016 more Obama circa 2006 or Paul in 2008/2012? It's too early to know.  As in, if Sanders is drawing 700 people at every event he does in Iowa and New Hampshire for the next six months, then we are having a different conversation that day than we are having today.

My guess -- and at this point it is nothing more than a guess -- is that Sanders will wind up being a slightly broader-based Paul.  He will be able to raise more money than most people guess and will continue to drive total loyalty within 20 percent (or so) of the Democratic electorate. That's enough to put a slight scare into Clinton. Nothing more.