First, the London interbank offered rate (commonly known as Libor) is going up. And second, the dollar's been going down.

Until mid-October, the relative performance of the Russell 2000 Index versus the S&P 500 Index loosely tracked the ratio of a basket of high-tax stocks compiled by Goldman Sachs versus their lower-tax peers. It made sense: Smaller firms tend to be more domestically focused than their larger-cap peers, and as such, were poised to benefit more from a decline in the U.S. corporate rate.

But around that time, three-month Libor costs started to surge, and ended up gaining 40 basis points in a little over three months. Soon thereafter, the Bloomberg Dollar Spot Index headed south, and proceeded to sink to its lowest level since the start of 2015 earlier this month.