For much of 2017, the dollar has been a disappointment among the major currencies, but there are signs that trend is reversing in the fourth quarter. The PowerShares DB U.S. Dollar Index Bullish Fund (NYSEArca: UUP), the exchange traded fund proxy for the U.S. Dollar Index (DXY), is up more than 2.2% since the start of the current quarter.

UUP tracks movements against a basket of currencies including euro, Japanese yen, British pound, Canadian dollar, Swedish krona and Swiss franc. The U.S. dollar is strengthening on a number of factors. For instance, the U.S. index of business conditions rose to a three-year high, adding to the improving U.S. economic outlook. Furthermore, Federal Reserve Chair Janet Yellen reaffirmed the central bank’s commitment to hiking rates, despite disappointing inflation results.

However, a strong dollar comes with some disadvantages, too.

“The greenback’s biggest decline in more than a decade has helped bolster profits at multinational companies like Apple Inc. (NASDAQ: AAPL) and Microsoft Corp. (NASDAQ: MSFT),” reports Bloomberg. “It’s one reason why stocks with high foreign sales currently are beating analyst estimates 57 percent of the time, while those with purely domestic revenue are doing it only 23 percent of the time, data compiled by Bank of America show.”

Although the dollar and UUP have struggled against the backdrop of two interest rate hikes by the Federal Reserve, some currency market observers see potential for the greenback to rally in the second half of 2017. The rising euro has also been a problem for the dollar, but some market observers believe the common currency is set to pullback.

Related: As USD Strengthens, Currency Hedged ETFs Require a Second Look

Obviously, UUP’s slack year-to-date showing indicates shorting the dollar has been the right way to play the U.S. currency. It may also imply that shorting the dollar has been easy. Moreover, the dollar’s 2017 struggles could be a sign that shorting the greenback is a trade with too many participants.

“But investors should beware of that benefit dissipating as the dollar reverses course. After bottoming in September, it has strengthened 4 percent against a basket of currencies. According to estimates by Goldman Sachs Group Inc., every 10 percent shift in the dollar affects S&P 500 Index earnings per share by $3,” according to Bloomberg.

For more information on the USD, visit our U.S. dollar category.