An 80-seat House battlefield?

(CNN)On Monday in California, the leader of the Koch brothers-funded Americans for Prosperity delivered a sobering message to the organization's donors: The 2018 midterms are going to be bad.

"You're going against the tide," AFP President Tim Phillips told the crowd. "You're going against history." 
Phillips added, "One last number I'll add: 80. That's the number of seats we believe that will be competitive in the end, this fall. Eighty. Math's not my strong suit, but these are daunting numbers."
Phillips' prediction of an 80-seat House playing field is, broadly speaking, in keeping with where non-partisan analysts see the state of play. The Cook Political Report counts 86 seats as competitive or potentially competitive while Inside Elections rates 67 seats as competitive.
    The problem for Republicans? Because of their massive gains in the 2010 and 2014 midterm elections, they have lots more seats to defend. Cook rates 66 Republican districts as competitive, as compared to just 20 for Democrats. Inside Elections puts 54 GOP seats in the competitive category and just 13 Democratic ones.
    It follows then that as the playing field gets bigger, Republican vulnerability rises. Which is why an 80-seat playing field this November would likely be curtains for the Republican majority. (Democrats need to net 24 seats to retake the House.)
    The best news for Republicans is that it's January 29. And the 2018 election is 281 days away. Politics -- especially in the age of Trump -- can pivot in a tweet, much less a month.
    "If it were today, I think we would win," House Minority Leader Nancy Pelosi, D-California, said in an interview with The Washington Post Monday. But she added, "It's not today."
    No, it is not. But, with Republican retirements -- 35 and counting with Rep. Rodney Frelinghuysen's decision not to run on Monday -- showing no signs of slowing, it looks like the playing field in November is going to get bigger, maybe much bigger.
    The Point: The number of competitive seats is getting bigger with each passing week. And it's an uneven growth, with Republicans looking at three times as many problematic seats to defend this fall. That's all bad news for Republicans' chances of holding their majority into 2019.