Don't be fooled: Tennessee changes nothing about the 2020 Senate map

(CNN)The first major surprise of the 2020 campaign came on Monday when Tennessee Sen. Lamar Alexander (R) announced he would not run for a third term in two years' time.

"I am deeply grateful, but now it is time for someone else to have that privilege," Alexander said in a statement.
There's a tendency when these sort of unexpected -- or at least un-leaked -- retirements happen to see them as events that fundamentally alter the chess board both parties are playing on in the never-ending fight over the Senate majority.
Some are! Most aren't. And Lamar's(!) retirement fits squarely in that latter category.
    Had he run for a third term, he would have likely won. His biggest problem would have almost certainly come in a Republican primary, where Alexander's pragmatic approach to governance -- a style that once made him a serious presidential candidate -- had riled some conservatives more closely aligned with President Donald Trump's confrontational conservatism. (Alexander beat back a primary challenger aligned with the tea party in 2014 although the little known candidate got north of 40% of the vote.)
    While his retirement -- and the open seat it creates -- might seem alluring for Democrats at first glance, the 2018 election results should beat that optimism out of them. In that race, Democrats nominated popular former Gov. Phil Bredesen, who polls showed running neck and neck with Rep. Marsha Blackburn (R) for months.
    But Blackburn wound up winning by 11 points despite Bredesen's popularity and a national wind blowing strongly behind Democrats. What that proved -- or should have proved -- is that the Volunteer State is effectively impenetrable for any Democrat -- even one as well-known and well liked as Bredesen. People forget just how Trump-y Tennessee was in 2016; the President Donald Trump won the state 61% to 35% over Hillary Clinton.
    Add it all up and you get this: Tennessee just isn't a terribly competitive state at the Senate level these days. (And that's even before the news broke the outgoing GOP Gov. Bill Haslam, who is very, very rich, is considering a run for the Lamar(!) seat.)
    The Tennessee seat doesn't change the basic math of the 2020 Senate map of which we already know a few things:
    1. There are 22 Republican seats (including Tennessee) up as compared to just 12 Democratic seats
    2. Of the 12 Democratic seats, two are in states Trump carried in 2016: Alabama and Michigan
    3. Of the 22 Republican seats, just two are in states Clinton carried in 2016: Colorado and Maine
    What's clear from those three facts is that while the raw numbers clearly favor Democrats in 2020, the actual states that make up the map are far less favorable for Democrats. Comparisons between this map for Democrats and the 2018 map for Republicans -- 25 Democrats seats up including 10 in states Trump won in 2016 -- aren't even close to fair.
    Republicans have lots more seats up, yes, but when you look at the seats that should be most vulnerable for the two parties, there's a lot more parity. The Alabama seat held by Sen. Doug Jones (D) is, without question, the most endangered seat held by either party; had Republicans nominated anyone other than Roy Moore in the 2017 special election, Jones would have never sniffed the Senate.
    That said, this map -- at least at it looks today -- is not inhospitable for Democratic gains. (The party needs to net four seats to retake Senate control if Trump holds the White House; they need a three-seat gain if a Democrat is elected president in 2020.)
    Colorado's Cory Gardner (R) will almost certainly face a serious Democratic challenge in a state Clinton won by 5 points in 2016. Ditto Rep. Martha McSally in Arizona who GOP Gov. Doug Ducey named Tuesday to replace Arizona Sen. Jon Kyl (R), who is resigning at the end of this year. Arizona Democrats are emboldened after Sen.-elect Kyrsten Sinema became the first Democrat since Dennis DeConcini to win a Senate race in the Grand Canyon State in 2018.
    Just below that level of vulnerability come a handful of GOP senators representing states where Democrats have had success at the federal level in the recent past or believe the demographics of the state are tilting their way: Thom Tillis in North Carolina, David Perdue in Georgia and Joni Ernst in Iowa.
    And, finally, two special cases.
    The first is Kentucky Sen. Mitch McConnell, the Senate's majority leader. McConnell has been in the Senate since 1984 but rarely wins by overwhelming margins due to his incredibly polarized image in the state. It's hard to see Democrats giving McConnell a pass in 2020, but his destruction of highly touted Democratic candidate Alison Lundergan Grimes in 2014 should serve as a warning to any opponent thinking beating McConnell will be easy -- or cheap.
    The second is in Maine, where Sen. Susan Collins (R) has long been assumed to be unbeatable despite the fact that the state has tended to favor Democrats at the presidential level in recent elections.
    Democrats argue all that changed when Collins provided the deciding vote to confirm Brett Kavanaugh to the Supreme Court earlier this year. That single vote, her opponents insist, crystallize the point they have been making for decades about Collins: She talks like a moderate but is always there when McConnell needs her on a critical vote.
    Everyone from former UN Ambassador Susan Rice to the speaker of Maine's state House have hinted that they might take on Collins, although it remains to be seen who actually makes the race.
      Outside of Jones in Alabama, the list of targeted Democratic incumbents is short. Republicans will give Michigan Sen. Gary Peters (D) a hard look given that Trump won the state in 2016. But Sen. Debbie Stabenow (D) easily dispatched a GOP challenger touted by Trump in