Janet Yellen should send a note of congratulations to Nigel Farage and Boris Johnson, the British politicians most responsible for pushing the Brexit campaign to a successful conclusion. While she's at it she should also send them some fruit baskets, flowers, Christmas cards, and a heartfelt "thank you." That's because the successful Brexit vote, and the uncertainty and volatility it has introduced into the global markets, will provide the Federal Reserve with all the cover it could possibly want to hold off on rate increases in the United States without having to make the painful admission that domestic economic weakness remains the primary reason that it will continue to leave rates near zero.

For months the corner that the Fed has painted itself into has gotten smaller and smaller. It continues to say that rate hikes will be appropriate if the data suggests the economy is strong. Then its representatives continually cite (arguably bogus) statistics that suggest a strengthening economy, which cause many to speculate that rate hikes are indeed on the horizon. But then at the last minute the Fed conjures a temporary reason why it can't raise rates "right now," but stresses that they remain committed to doing so in the near future. But each time they conduct this pantomime, they lose credibility. Sadly, Fed officials are discovering that their supply of credibility is not infinite, even among those who would like to cut them a great deal of slack.

But the Brexit vote saves them from all this unpleasantness. Now when critics question the Fed's unwillingness to deliver on the suggested rate hikes, given what they believe to be a strong economy, all the Fed needs to do is point to the "uncertainty" that will be in play now that the world's fifth largest economy is disengaging from the European Union. And since this process is bound to be long, messy, and fraught with uncertainties (as there is no precedent for a country leaving the EU), this will be a handy excuse that the Fed will be able to rely on for years.

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Brexit could also place severe strains and uncertainties on the global currency markets. The fear of financial losses could encourage investors to seek safe haven assets like gold and, at least for now, the U.S. dollar. Given that there is already much concern that the dollar is valued too highly against most currencies, and that this has created imbalances in the global economy, any surge in the dollar that results from Brexit may have to be fought by the Federal Reserve through lower interest rates and quantitative easing. This would rule out the potentially dollar-strengthening interest rate hikes that they supposedly planned on delivering. So as far as Janet Yellen is concerned, the British have given her the gift that keeps on giving.