WASHINGTON — The United States posted strong economic growth in the third quarter, but the Fed's preferred inflation gauge also accelerated, the Commerce Department said on Thursday, in a mixed economic bag for U.S. President Donald Trump ahead of key midterm polls next week. Real GDP increased at an annual rate of 3.4 percent in the third quarter, the department's Bureau of Economic Analysis (BEA) said in a statement, beating market expectations. "The contributors to the increase in real GDP in the third quarter were increases in investment, consumer spending, and government spending that were partly offset by a decrease in exports," the BEA said in a statement. The U.S. Federal Reserve's preferred gauge for inflation — the Personal Consumption Expenditures (PCE) price index — rose by 3.6 percent year-on-year in September, an increase from the previous month. Trump's handling of the economy is a key issue for voters heading into midterm elections on Tuesday, where Democrats are seeking to wrest control of both houses of Congress from the president's Republican Party. The U.S.-Israe