A first look at the 2020 Senate map: Republicans have a good shot at maintaining control

(CNN)Voter enthusiasm for the 2020 presidential election is already sky high. With all the coverage of Beto O'Rourke's counter climbing and Pete Buttigieg's speaking approximately 200 languages, you might forget that 34 Senate seats are also up for election. You can bet those races will soon be hotter than a firecracker, given the Senate's power to confirm Cabinet members and federal judges -- such as the justices who sit on the Supreme Court.

Republicans have a better shot than not of maintaining control of the Senate in 2020. However, recent trends indicate that the possibility of a clean sweep for either side (i.e. taking the presidency and the Senate) is higher than it's ever been.
Democrats need only a net gain of three Senate seats to win control, if they win the presidency. In such a case, the vice president would break the tie. With Republicans controlling 22 of the 34 seats up for election, Democrats have, in theory, a wide playing field from which to choose.
    The problem for Democrats is that the biggest trend in Senate elections is straight ticket voting. When you cast a ballot for one party on one part of the ticket in recent elections, the chance of voting for that same party on other parts of the ticket is significantly higher than it used to be.
    An astounding 87% of the differences in the Senate margins across states could be explained by the statewide aggregate House margins in 2018. Ergo, if you voted for a Democratic (Republican) candidate for the Senate last year, there was a very high likelihood that you voted for a Democratic (Republican) candidate for the House.
    The same pattern is apparent when comparing the Senate results last year with past presidential election results across states. States that leaned Democratic (Republican) in past presidential elections were far more likely to vote Democratic (Republican) in Senate races last year. The Senate and last two presidential election results were more simpatico in 2018 than Senate and past presidential results had been in any midterm election since at least 1982.
    This comes on the heels of 2016, when every state that sent a Republican to the Senate voted for Republican Donald Trump and every state that sent a Democrat to the Senate voted for Democrat Hillary Clinton. In no other presidential year in the last 100 had this phenomenon (of all states voting the same for Senate and presidency) occurred.
    So how does that shake out for the 2020 map?
    Of the 22 seats controlled by Republicans, just two of them are in states (Colorado and Maine) that leaned Democratic compared with the nation as a whole in a weighted average of the last two presidential elections (75% in 2016 and 25% in 2012). Today, President Trump is quite unpopular in both. Additionally, both states were very Democratic in the aggregate House vote in 2018.
    Now, they certainly aren't gimmes, given that both states were within 5 points in the last presidential election. Still, Democrats have clear pickup opportunities in Colorado and Maine, for the seats now held by Sens. Cory Gardner and Susan Collins, respectively.
    Therefore, you would think that Democrats were just one seat away, if things went well in Colorado and Maine.
    Here's the complication: Alabama. You may recall when Democrat Doug Jones shocked political analysts and pundits by beating very flawed Republican Roy Moore in a 2017 special election. Now that seat is up again. The good news for Democrats is that Moore, who faced sexual abuse allegations and had an archconservative record, may be running again. But even if Moore won the nomination (and chances are he won't), Jones wouldn't benefit from depressed Republican turnout this time around, because Trump will be on the ballot.
    Alabama is a state Trump won by nearly 30 points and remains popular in. Republicans won the aggregate House vote there in 2018 by more than 20 points. That means Jones has an uphill climb for re-election by the numbers.
    In other words, even if Democrats pick up Colorado and Maine, they'd probably be looking at a net gain of one.
    Beyond these seats, the Democratic pickup opportunities slim dramatically. Of the other 20 Republican-held seats up for election, 16 of them are in states that were 10 points or more Republican than the nation as a whole in a weighted average of the last two presidential elections. None of these races look competitive at this time.
    The other four have leaned 5 to 10 points more Republican than the nation in a weighted average of the last two presidential elections: Arizona (Martha McSally), Georgia (David Perdue), Iowa (Joni Ernst) and North Carolina (Thom Tillis).
    It's conceivable that Democrats could win in these states. They just won a Senate election in Arizona against McSally, who was appointed to her Senate seat following her defeat in the race for the other one. The statewide 2018 House votes in all these states were close. The best Republican state