Democratic presidential candidate Sen. Bernie Sanders, I-Vt., speaks at a rally, Sunday, Aug. 9, 2015, at the Moda Center in Portland, Ore. (AP Photo/Troy Wayrynen)

The photo above is what 19,000 people packed into a basketball arena to hear Vermont socialist/independent Sen. Bernie Sanders looks like. What you don't see are the 9,000 other people who couldn't get into the arena but listened on loudspeakers outside.

That was the crowd that gathered on Sunday in Portland, Ore., to hear Sanders speak -- the largest gathering of a presidential bid that has made its name on its big crowds.

"Portland, you have done it better than anyone else," Sanders said at the speech of his one-hour (!) speech, according to the Oregonian.

I've written before about the Sanders' crowd phenomenon -- and how hard to know what it means (if anything). Portland is a known den of progressivism where President Obama drew massive crowds during his 2008 campaign; an estimated 75,000 people showed up for a rally in May 2008 for Obama.

But, 28,000 people! In August! Of an off year! I mean, that is a lot. A LOT.

Bernie Sanders's presidential campaign says the Democratic candidate drew 28,000 people — its largest crowd yet — in Portland, Ore., on Aug. 9. (Sarah Parnass/The Washington Post)

Ask yourself this: If Hillary Clinton announced a rally next weekend in, say, Seattle, could she get 28,000 people to show up?  Maybe. But it's far from a sure thing that she could.

Now, Portland is Portland. And Oregon isn't going to be a decided factor in the Democratic presidential primary process.  (The primary will be May 17 and, yes, I had to look that up.) And, most polling -- with the exception of New Hampshire -- suggests Clinton has very little to worry about in a Democratic primary.

But, crowds are at some level an indicator of organic energy -- it is after all how it became clear in 2006 and 2007 that something major was happening with Obama. And, one of Clinton's biggest problems is -- you guessed it! -- the perception that her candidacy lacks energy.

Clinton isn't in the danger of losing the Democratic nomination that she was in 2008. But lack of passion (or even a perceived lack of passion) is dangerous for her regardless of how serious a candidate Sanders winds up being.  Republican base voters will be fired up beyond belief to take back the White House -- and vote against Clinton -- next November. She has to find ways to create that passion for herself within the Democratic base.