What you said here troubles me and it may simply be the way it's written... I just read the instructions for IRS Form 8300 at this link. The instructions for the form read:

"Who must file. Each person engaged in a trade or business who, in the course of that trade or business, receives more than $10,000 in cash in one transaction or in two or more related transactions, must file Form 8300. Any transactions conducted between a payer (or its agent) and the recipient in a 24-hour period are related transactions. Transactions are considered related even if they occur over a period of more than 24 hours if the recipient knows, ..." (emphasis mine)

Notably, it says: "...receives more than $10,000 in cash..." and then it also says:

"Voluntary use of Form 8300. Form 8300 may be filed voluntarily for any suspicious transaction (see Definitions on page 4) for use by FinCEN and the IRS, even if the total amount does not exceed $10,000..." where "A suspicious transaction is a transaction in which it appears that a person is attempting to cause Form 8300 not to be filed, or to file a false or incomplete form..."

So, where I read you saying "$10,000 or less must be report on IRS form 8300" I trust you're not saying "if you have transaction of less than $10,000 and think it might look like a "suspicious transaction" the way to report that transaction is on form 8300" not that one MUST report all cash transactions, even those under $10,000, right?

Now, going back to the topic at hand, one might argue that Steve Bierfeldt had an amount of cash which was less than $10,000 and could have then voluntarily reported that on behalf of the political campaign if it would appear that he was trying to circumvent the filing of that form by carrying less than $10,000 (i.e.: multiple cash transactions of $9,999.99) BUT in Bierfeldt's case his possession of about $4700 is nowhere near $9,9999 AND that sum was given him in multiple smaller transactions (i.e.: bumper sticker sales).

So, just so we're clear, (and while I'm not suggesting that's what sfspec is actually suggesting), I can't see where filing or not having filed something like Form 8300 or its provisions supports any reasonable suspicion on the part of the TSA guy in the underlying Bierfeldt incident.