After an initial record surge in the amount of US corporate cash repatriated from offshore jurisdictions (if only for accounting purposes, as the bulk of said cash was already largely invested in domestic securities via offshore entities) following Trump's tax law overhaul and tax repatriation holiday, the movement of foreign cash has slowed sharply.

This comes at a time when record notional corporate buybacks have not only surpassed total capex spending for the 2nd quarter in a row, but have been seen as responsible for the relentless bid supporting the stock market.

So why are offshore fund flow important?

Because, as many strategists have noted over the past year, with JPMorgan's Nikolaos Panigirtzoglou doing so most recently in his latest Flows and Liquidity report over the weekend, US repatriation flow are a key leading indicator for US stock buybacks.

And the problem for stock market bulls, is that recent data are consistent with this idea that offshore cash repatriation is slowing considerably and by implication, so are buybacks.