(CNN) Doug Jones' stunning victory in Alabama on Tuesday night sent a very clear signal heading into the 2018 election: No Republican Senate seat is safe.

What that means is this: Democrats now have a reason to believe that they could do something that was considered unthinkable as recently as the start of this week: Retake control of the Senate next November.

"The favorable map makes Democratic gains more challenging, but it's not just about geography, but also about voters," said GOP pollster Glen Bolger. "The electorate does not give political parties a long leash on control."

That map to which Bolger refers was seen at the start of this election cycle as definitive proof that Democrats wouldn't even sniff the majority for years to come.

Democrats have to defend 26 seats (two of which are held by independents) next November as compared to just eight for Republicans. Of those 26 seats, 10 are in states that Trump carried in 2016 -- including five that he carried by double digits. (The reason Democrats are defending 26 seats instead of 25 is that Sen. Al Franken has promised to resign in the wake of multiple groping allegations and there will now be two Senate seats on the ballot in Minnesota.)

Read More