The U.S. presidential election is back at the top of currency traders' list of worries.

After the revelation last week that the Federal Bureau of Investigation is reopening its inquiry into Hillary Clinton's use of private email, implied volatility in two-week options in the dollar-yen exchange rate timed to the Nov. 8 vote climbed to the highest levels since September, according to data compiled by Bloomberg. The foreign-exchange market had been looking past the campaign, putting greater emphasis on global central bank meetings in December, when the Federal Reserve is forecast to raise interest rates.

Sentiment in the currency market shifted after the FBI's Oct. 28 announcement shattered a period of relative calm. Investors had been betting a likely Clinton victory would prompt the U.S. to uphold global trade agreements denounced by rival Donald Trump, who has also called for tighter immigration controls. Clinton's odds of victory have fallen to 75.6 percent, according to poll aggregator FiveThirtyEight, from 81.6 percent last week, while traders on online betting market PredictIt give Clinton a 71 percent chance of winning the election, compared with 81 percent on Oct. 19.