Republican Sen. Ted Cruz, of Texas, sought to fend off an underdog challenge Tuesday from Democratic Rep. Colin Allred in one of the year's most expensive races, which is testing shifts in America's biggest red state and could factor into the fight for U.

The U.S. Senate showdown between Republican Ted Cruz and Democrat Colin Allred is one of the most watched Election Day contests in the nation, and its result will play a role in determining which party controls the Senate.