Addressing the prospect of Republican leadership in both chambers, Jack Ablin, chief investment officer at BMO Private Bank, said, "My sense is it will only harden the tension that's in place." Boles noted that tax reform "faces long odds in any Congress" but has a better chance of reaching Obama's desk with a Republican Senate than with the currently divided Congress. Proposals to lower corporate tax rates, for instance, and allow companies to bring back profits from abroad without incurring significant taxes could fuel growth, its supporters say. The Democrats hold a 55-45 edge in the Senate, meaning that Republicans need a net gain of six seats to take control of the chamber. Many candidates of both parties are running against Obama, whose approval rating has slumped to 41 percent among likely voters compared with 49 percent heading into the 2012 election, according to polling last month by The Associated Press. In a TV ad in North Carolina, Republican challenger Thom Tillis accused Democratic incumbent Kay Hagan of being a "rubber stamp" for the president. The 2011 battle over a debt ceiling increase caused financial markets to plunge and triggered a first-ever downgrade in the U.S.