Unpacking the real story behind Republicans' chances at holding the Senate in 2018

(CNN)On Sunday, The New York Times published a piece headlined "Senate Republicans Are Newly Hopeful About the Midterms. For Good Reason." The argument in the piece, as the headline suggests, is that Republicans are -- and should be -- optimistic about their chances of holding (and maybe even expanding) their one-seat majority.

Is that right? Chris reached out to CNN big brain -- and election nerd -- Harry Enten to chat about the state of the Senate. Their conversation, conducted via email and lightly edited for flow, is below.
Cillizza: Dearest Harry.
I assume you are stockpiling A&W products in advance of tomorrow's California primaries.
    If you can take a break from that caffeination campaign, I wanted to talk about the NYT piece from Sunday that argues that Senate Republicans are in a better place than they have been in a while in their hopes of holding the Senate this fall.
    The piece hangs that optimism on two things: Eric Greitens (finally) resigning as governor in Missouri and John McCain remaining in the Senate long enough to avoid his seat being on the ballot in November.
    All of which got me to thinking about the crazy expectations arc of the Senate race so far. The 2018 election began with Republicans talking (quietly) about the possibility of winning a filibuster-proof 60 seats after 2018. Then, as Trump's numbers tanked and he got more and more unpredictable, Republicans openly worried that the majority could be in play. Those worries only got worse after Doug Jones beat Roy Moore late last year in Alabama. And now, optimism.
    Where are you today on Republican chances of keeping their Senate majority?
    Enten: Chris Dear.
    I think I'm going to have some A&W during this conversation, if that is okay with you. You're more than welcome to share in the natural goodness that is this fantastic diet soda.
    My, oh my, haven't the goalposts shifted in some quarters since the beginning of the cycle. Congrats on your guy not being totally and completely tied to a governor who needed to resign in disgrace!
    I think you need to keep a few things in mind when talking about the Senate. The first is, obviously we're dealing with a very stacked playing field. Democrats control 26 of the 35 seats up. Ten Democratic incumbents are running in seats Donald Trump won in 2016. That would point to a very wide playing field for the Republicans.
    The second is it's very difficult for incumbents to lose in a midterm when their party doesn't control the White House. These incumbents have gone 110 for 114 since 1982. Even in states that lean toward the president's party, these incumbents are 39 for 42.
    These are the two colliding forces, and I think you're seeing that play out across the board. In Missouri, for example, we've seen why it's so hard to get (Missouri Sen. Claire) McCaskill down, even though Trump won the state by nearly 20 points.
    There are other races where that is clearly true as well. And a few where the Democrats have a real shot of a pickup...
    May Fudgie always be with you,
    Harry
    Cillizza: Fudgie the Whale is the greatest ice cream cake creation of all time. I will fight anyone who disagrees.
    But back to the Senate -- although I could do a whole riff on the joys of Carvel. (As I know you could also.)
    I think the Alabama special may have been taken as too much of a "rule" rather than an exception by Democrats. Yes, Doug Jones won in a state that was -- and is -- overwhelmingly Republican. Which, in theory, makes Democrats potentially competitive anywhere in the country. (Also, relatedly: "In theory, communism works." -- Homer J. Simpson)
    The problem with that logic is that Republicans aren't dumb or incompetent enough to nominate someone as bad as Roy Moore in every -- or any? -- Senate seat this fall. With even a moderately damaged OP candidate, Jones probably loses -- even with the clear energy and passion coursing through the Democratic base. Moore was just so bad and so damaged that he couldn't drag himself across the finish line.
    While Republicans don't have perfect candidates in North Dakota or West Virginia or Missouri, each of those candidates are credible. None of them are Roy Moore or anything close. So, assuming that Alabama tells us everything we need to know about the state of the two parties in the 2018 Senate races is a mistake.
    In short: I think Alabama made Democrats overly exuberant and Republicans far too pessimistic. With that race now six months in the rear-view mirror, I think expectations are settling back into a more normal place: Republicans have major structural edges that will be tough for Democrats to overcome even in a national environment where the Republican president is polling in the low 40s.
    Yes? No? Maybe so?
    Enten: When I was a kid, I used to get a non-fat Carvel chocolate soft-serve every Friday night. I thought I was being healthy. Of course, I also added the full-fat hot fudge, whipped cream, chocolate crunchies, chocolate sprinkles and cherry on top.
    Extrapolating out from Alabama is like picking out the 2017 Buffalo Bills and saying that's how things have gone and will go for the franchise. We all know though that the Bills won't make the playoffs for another 264.3 years, unfortunately :(
    Look, the GOP has good enough candidates in all those races. In some of them, they have good candidates. But you know I'm a numbers guy. You know that. Where is the proof that the Democrats cannot win all those races you describe?
    There is barely any public polling in those races you mentioned. The polling I do see suggests that most of those races are tossups for the GOP at best. Now, we have a campaign season to go, so things may change.
    But I do wonder if we're all guilty of having a similar problem that you're describing about those who look at one race (Alabama Senate) and decide that's the rule going forward.
    We all believe that because these states (e.g. Indiana and Missouri) went heavily for Trump, and there's been an increasing tie between Senate and presidential outcomes during the Barack Obama administration, that Democrats may be screwed. Maybe that's right. Maybe. But that link really between Senate and presidential results didn't exist in 2006 when the Democrats took back the Senate.
    We've seen Democrats do very well in a lot of special elections (though less so recently) in some not-so-friendly places (e.g. Pennsylvania 18). Maybe the correlation between presidential and Senate outcomes won't really be there in 2018.
    So I answer your question with a maybe. Or better put, I answer it with a "I don't know" and "to be determined."
    I'm drinking a diet soda right now.
    Cillizza: I drink only coconut milk.
    Now, to your point -- which to me is THE critical question of 2018: Is the Trump coalition a) sustainable and/or b) transferable?
    In Alabama and, especially, Pennsylvania 18, Trump went in hard for the Republican nominee -- arguing, essentially that if you like Donald Trump you will like Roy Moore and Rick Saccone. Both of those people lost -- in a seat and a state where Republicans should win easily.
    What does that mean? Does it mean that Trump is sui generis? That the Trump coalition works for Trump and no one else? Does it mean that the Trump 2016 coalition no longer exists? What if it just means that these were two special elections that tell us nothing about Trump's appeal in the fall?
    Enten: I remember one person told me I'd like coconut water because I liked coconut milk. What a disaster.
    Now, this is the ultimate question of the midterms: What impact does Trump have?
    I mean this in multiple ways.
    First, are the areas where Trump did better than Mitt Romney going to continue to be places where the GOP can overperform? And on the flip side of that, are places where Trump underperformed Romney places where the Democrats can overperform? Evidence so far is quite mixed in my opinion. I'm not exactly sure.
    In the Senate, this could mean that maybe we're overestimating the Democrats' chances in Arizona, which was a state that swung toward them with Trump on the ballot. On the other hand, maybe Joe Donnelly has a better shot of holding on in Indiana.
    Second, can Republicans run ahead of Trump? That is, maybe Trump's unpopularity doesn't transfer over to congressional Republicans. I tend to doubt that, but it's plausible.
    And on that point, what happens when you're in a red state where Trump isn't all that popular? Does the normal Republican lean of those districts keep the Republicans in play there?
    The truth probably lies somewhere in between on all of this stuff. Again, I go back to what I said earlier. If people vote on their feelings toward Trump, it's difficult to imagine Democrats picking up the Senate. If, however, they vote for incumbents (which they normally do), Democrats have a real shot.
    I'm ordering an ice cream.