(CNN) Sen. Thad Cochran announced Monday that he will vacate his seat on April 1, setting up a special election in Mississippi that will take place on Election Day in November.

Republicans are favored to hold on to the seat in a state as red as Mississippi. President Donald Trump won it by 18 points. No Democrat has won a Senate race there since 1982 or a governor's race since 1999. Mississippi is also a state where there isn't a lot of elasticity in the electorate (i.e. voters don't tend to shift around).

So should Democrats dismiss the possibility they could win in the Magnolia State? I don't think so.

Here's why: Democrats should keep an eye on any state where Trump is barely above water and where a weak general election candidate may end up being the Republican choice against the Democrat.

To start, there is a single digit spread in Trump's approval and disapproval ratings in the state. A December Mason-Dixon poll gave Trump just a 51% approval rating to a 43% disapproval rating among voters in the state. Gallup's polling over the course of 2017 among adults in Mississippi put Trump's approval rating at only 48% to a disapproval rating of 46%.

These spreads are far smaller than the spread between Trump and opponent Hillary Clinton in the 2016 presidential election.

Trump's approval rating suggests that a single digit race is quite possible in the state. The generic ballot does as well.

Right now, Democrats are ahead by about 10 points nationally in the average survey. In CNN's poll, they're up 16 points. History tells us that the average Senate seat with no elected incumbent should shift in-line with the national environment as depicted on the generic ballot.

Weighting the past two presidential results in a way that best explains the special election results so far this year, Mississippi is about 16 points more Republican than the nation as a whole.

Even if we use the average generic ballot result, the fundamentals suggest Mississippi could be competitive. The CNN poll indicates it could be very competitive.

Another factor will be who the candidates on the ballot are in November. The rules in Mississippi are such that there will be a primary on Election Day in which candidates of all parties run together, and, if no one reaches 50%, a runoff is held. This "jungle" primary makes predicting who might face off in a runoff difficult to predict. Turnout for runoffs is also difficult to predict.

If only one Republican candidate makes the runoff and it's a very conservative candidate like Chris McDaniel, for example , Republicans could be in a world of trouble. (McDaniel is currently running against Roger Wicker for the state's other Senate seat, though he could switch races.) Back in 2014, when Democratic President Barack Obama was unpopular, some polling showed that McDaniel was actually in danger of losing a hypothetical matchup against Democrat Travis Childers. With Obama not weighing down Democrats in 2018, it's not hard to imagine a close race with someone like McDaniel on the ballot.