If his supporters come out in large enough numbers to deliver him victory, it will prove beyond doubt that the Trump phenomenon is real. It will also mean that his march toward the nomination will be hard to stop.

Just the opposite could happen, too. A loss for Trump would suggest that his brio and personal celebrity is not backed by enough organizational muscle to get results.

Which will it be? Even experts steeped in Iowa Republican politics admit they simply don’t know.

Matt Strawn, who served as chairman of the Republican Party of Iowa from 2009 to 2012 says there is a “giant, Trump-sized question mark” about whether the people who profess support for the business mogul will show up.

“There are these large, sweeping crowds but what kind of mechanism has the campaign created to turn those event-attenders into caucus-goers?” asked Strawn, who is not affiliated with any candidate’s campaign.