Here we go again. Where in the federal register is it a crime to have a large sum of money in your possession?
It not a crime. Not even when that money is a very large amount of cash, consisting of bills of small denominations, with traces of cocaine residue, wrapped in aluminum foil, in a plastic bag, in a cooler, in the backseat of a car rented by a unknown individual (not the driver), driving 2000 miles from a "drug destination" state to a "drug source" state.
What it IS is suspicious and indicative of drug activity, especially when combined with other factors -- the main one being a believable explanation for it.