Washington (CNN) Republican Rep. Ryan Costello's weekend announcement that he won't seek re-election in Pennsylvania makes the 6th District seat in the Philadelphia suburbs look like even more favorable ground for Democrats.

Already, this seat was leaning in their direction. The Pennsylvania Supreme Court's decision to scrap the old, gerrymandered congressional map and replace it with a new one this fall meant Costello's Chester County district had shifted from one that split almost evenly between Hillary Clinton and Donald Trump in 2016 to one that favored Clinton by nearly 10 points.

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Costello, though, was a young and talented incumbent. He gave Republicans a fighting chance in the district. He acknowledged Sunday that redistricting and the tough political headwinds Republicans face with an unpopular Trump were factors in his decision to retire.

"The combination of what I've had to deal with just in terms of having a young family, what the state Supreme Court did, which I think was obscene, along with the political environment, has led me to the decision that what is best for my loved ones, that at this moment in time, running for reelection is not the prudent course of action," he told MSNBC's Kasie Hunt.

Democrats have a candidate they like in former nonprofit executive Chrissy Houlahan, who has already proven to be a strong fundraiser, outraising Costello in 2017's fourth quarter.

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