Editor's Note: There are just 70 days until Election Day, and the NBC News political unit each day will profile the most competitive races this midterm season.
This is the “canary in the coal mine” race, with its relatively early poll-closing time (8:30 pm ET). A win by incumbent Sen. Mark Pryor (D) would signal that Democrats are well-positioned, even in a state like Arkansas, to hold their Senate majority. Conversely, a win by opponent Rep. Tom Cotton (R) -- a rising star in the party -- gets Republicans one step closer to Senate control. Helping Pryor is his last name (his father David is the state’s former governor), as well as Cotton’s inexperience (he was elected to the House in 2012). Helping Cotton is the state’s GOP-leaning nature (Obama won just 37% of the vote in ’12), as well as midterm electorate (when fewer members of the Democratic base turn out). Polls so far have shown that the race is a coin flip.