(CNN) As the calendar nears 2018, the battle for control of the Senate is shifting in all sorts of unexpected ways -- changes driven primarily by bad behavior but also a national political environment heavily colored by President Donald Trump's widespread unpopularity.

Consider this series of recent developments:

These three moments don't all work in one party's favor. A Jones win coupled with Bredesen's candidacy would clearly give Democrats momentum. The Franken resignation takes a seat that wouldn't even be on the map in 2018 -- his term isn't up until 2020 -- and makes it a problem that Democrats have to deal with in a year when they are already defending more seats than Republicans.

This series of events lands in what has already been a very unpredictable Senate election cycle. On its face, 2018 should be a banner year for Senate Republicans, with just nine seats to defend and 25 Democratic seats (not counting the now-open Minnesota seat) to target. Of those 23 Democratic seats, almost half -- 10 -- were carried by President Trump in 2016 including five (Indiana, Missouri, Montana, North Dakota, West Virginia) where Trump won by double digits.

It hasn't turned out that way -- yet! -- for Republicans as Trump's unpopularity has created a national political environment where Democratic candidates are coming out of the woodwork to run while top-tier Republicans are more hesitant to do so.

In Montana and North Dakota, two strongly Republican states represented by Democrats, Republicans have yet to land an "A"-type candidate. In Indiana and West Virginia, there are crowded primaries on the Republican side that will likely be nasty and expensive even before a dime is spent on the Democratic incumbents.

Arizona Sen. Jeff Flake into retirement and leading Nevada Sen. Dean Heller to And Steve Bannon-backed primary challengers are making life difficult for Republican incumbents, chasingSen. Jeff Flake into retirement and leadingSen. Dean Heller to brag that he "helped write" a tax bill that's widely unpopular.

Florida Gov. Rick Scott -- who Republicans hope will run against Democratic Sen. Bill Nelson next year -- put the heartburn Trump is causing even his staunchest allies in perspective when asked at a Republican Governors Association meeting last month whether Trump will help or hurt GOP candidates in the midterms. "We'll see what happens in 2018," Scott said.

Would he want Trump to campaign for him in Florida? "I don't know if I'm going to be a candidate. We'll worry about that next year," Scott said. Can Trump help Republicans on the ballot next year? "You'd have to ask them."

Not exactly a ringing endorsement.

The 2018 cycle started with Democrats expecting to play defense across the board. There were just too many seats to defend, and only two pickup opportunities (Arizona and Nevada) when they need to add three seats -- and hold onto all of their own -- to take control of the Senate.

If you asked Republicans at the start of the 2017 whether it was more likely that they would lose their majority or wind up with 60 seats at the end of 2018, they would have chosen the latter option every single time.

Now, the Senate majority looks in play -- even if Republicans still retain an edge due to the sheer number of Democratic seats in play and where those seats are.

If Jones wins next Tuesday in Alabama or Bredesen can turn Tennessee competitive -- and Trump stays unpopular -- the stakes get a lot higher. Add in Minnesota and the playing field is even bigger and less predictable.

It's not immediately clear whom that heightened unpredictability benefits. But Democrats surely never expected to be even sniffing at talk of regaining the Senate majority come 2019. And, for now, that's a possibility you wouldn't get laughed out of the room for bringing up.