The battle for power in the Senate tightened into Wednesday as Democrats picked up a seat in Colorado, but suffered a setback in Alabama, and Republicans held their own in high-profile races in South Carolina, Iowa, Texas and Kansas, dramatically narrowing the political map. Republicans fought to retain their Senate majority by turning back a surge of Democrats challenging allies of President Donald Trump, and the Democrats’ various paths to seizing control were growing more limited. With several contests still too early to call, and one Georgia race heading to a January runoff, the final verdict is expected to drag on. Democrats gained a seat when ex-Gov. John Hickenlooper ousted GOP Sen. Cory Gardner in Colorado, a must-win to flip the Senate, but couldn’t hold on in Alabama, where forme...