WASHINGTON - A new poll shows Rick Santorum and Mitt Romney running even at the top of an increasingly challenging Republican race to unseat President Barack Obama in November, with their latest debate Wednesday night ushering in a new and more perhaps intense round of primary voting. Obama has been seen as vulnerable on economic issues, but his numbers are rising as the economy shows signs of recovery from the Great Recession. Obama tops 50 per cent support when matched against each of the Republican candidates and holds a significant lead over each of them, according to the Associated Press-GfK poll. With the unemployment rate inching down and manufacturing and construction improving, the Republicans have turned toward social issues as a line of…