In the 2008 Election, Tennessee was the third-most populous state to vote for John McCain. This is important for two reasons: Tennessee represents a gigantic chunk of Republican base voters, and because of the Republican delegate allocation rules, it has a larger share of delegates than a Democratic-voting state its size.
Before Super Tuesday, 12 states had held contests, with 9 of them being states Obama won in 2008, while only 3 of them being McCain states. On Super Tuesday, of the 10 states voting, 6 of them were McCain states and 4 of them were Obama states. Georgia and Tennessee were the largest of these, the first large test of how well Romney, the front runner, could do in Republican base country.
If you had asked me, weeks prior to the contest, I would have said that Tennessee was a natural state for Newt Gingrich, the natural candidate for the south. But my expertise on Tennessee amounts to spending less than 24 hours in the state, and my visit to the Tennessee Greyhound station probably doesn't qualify me as an expert on all things Tennessee. Someone could perhaps explain to me the gradations between the Deep South and Border States, but then, after almost 300 years of American history, maybe it is beyond explanation. In any case, Rick Santorum, the leading conservative alternative to Mitt Romney, was ahead in polling in Tennessee. Although it had almost as many delegates as Ohio, it was not as heavily polled, and it looked possible for any one of the three major candidates to win the state.
On election night, it was Santorum however who would win the state. He garnered 37% of the vote, against 28% for Mitt Romney and 24% for Newt Gingrich. In addition, he won all but three of the state's counties: Nashville and one of its suburbs went to Romney, and a single county on the Georgia border voted for Gingrich.
Tennessee gave Santorum many delegates, but it also gave him a good sign that he would do well in other southern states, including, of course, Texas, with its gigantic share of delegates. The state was probably the most disappointing for Newt Gingrich, who finished third in a southern state that should have been, if not a stronghold, at least a competitive state. Whether Santorum can consolidate in the south, and use the region's disproportionate number of delegates to defeat Gingrich is one of the many questions raised by the Tennessee victory, along with other contests on Super Tuesday.