Corrected Sunday 12:54 a.m. | On paper and in theory, Republicans’ chances of winning back the House look pretty good. But a district-by-district analysis reveals much longer odds, even if the Democrats nominate Bernie Sanders for president.

Republicans need a net gain of 18 House seats for the majority. Considering 30 Democrats represent districts President Donald Trump carried in 2016, it would appear the GOP is well-positioned for a takeover.

In reality, the number of seats Republicans need to gain is closer to 21 because the party is likely to lose two seats in North Carolina under its new district lines, as well as Rep. Will Hurd’s seat in Texas. In addition, not all of those 30 Trump districts are currently hosting competitive races.

[See all race ratings by Inside Elections]

With a combination of poor GOP recruitment and strong fundraising by Democratic incumbents, Inside Elections recently downgraded Republicans’ chances of victory in nine districts, including three Trump seats held by Democrats whose reelections no longer appear on the list of competitive races at all. Those contests — Angie Craig’s in Minnesota’s 2nd, Mikie Sherrill’s in New Jersey’s 11th, and Ron Kind’s in Wisconsin’s 3rd — all moved from Likely to Solid Democratic.

Two more Trump-district Democrats — Elissa Slotkin in Michigan’s 8th and Antonio Delgado in New York’s 19th — are also looking stronger. They’ve been upgraded to Likely Democratic from Leans (Slotkin) and Tilts (Delgado).

Also moving into the Solid Democratic category from Likely are two Democrats in districts Hillary Clinton carried in 2016: Ann Kirkpatrick in Arizona’s 2nd and Sean Casten in Illinois’ 6th.

That all narrows the list of legitimate GOP takeover targets.

At the same time, two more GOP-held seats are looking more vulnerable for very specific reasons. They include Florida’s 15th, where GOP incumbent Ross Spano’s bid for a second term moves from Solid to Likely Republican; and Michigan’s 3rd, where Republican-turned-independent Justin Amash sees his race move from Leans to Tilts Republican.

It’s not all bad news for Republicans. Recent rating changes by Inside Elections improved the GOP’s chances of winning in six districts, including two seats no longer listed on the House battleground. Those districts and the shift from old to new ratings are as follows:

• California’s 25th (Vacated by Democrat Katie Hill’s resignation): Solid D to Likely D
• Florida’s 26th (Democrat Debbie Mucarsel-Powell): Solid D to Likely D
• Kentucky’s 5th (Republican Andy Barr): Likely R to Solid R
• Minnesota’s 8th (Republican Pete Stauber): Likely R to Solid R
• North Carolina’s 9th (Republican Dan Bishop): Leans R to Likely R
• Texas’ 31st (Republican John Carter): Leans R to Likely R

Even if Democrats nominate Sanders for president, which supporters of other Democratic contenders say would put the party’s House majority in danger, there’s no guarantee GOP chances will dramatically improve because his effect isn’t likely to be universal.

The Vermont senator’s brand of populism could resonate better in the Rust Belt, a key geographic area where Republicans need to win a couple handfuls of seats and where the party has struggled to find quality challengers. Sanders could be a liability in the suburbs, but that is also where Democrats have some of their strongest freshman members, who will be able to outspend their GOP challengers by multiple factors.

Instead of assuming a Sanders nomination would be a game-changing national event, it’s probably best to wait for data in individual districts that can provide a window into specific races that account for unique dynamics.

More detailed analysis of more than 75 House races is available in the Feb. 21 issue of Inside Elections.

Nathan L. Gonzales is an elections analyst with CQ Roll Call.

Correction: An earlier version of this story misidentified the congressman for Texas’ 31st District.