CNN key House races: New Pennsylvania maps help Democrats in several districts

Washington (CNN)The Pennsylvania Supreme Court gave Democrats a boost in their effort to gain control of the House this week when it unveiled new congressional district maps and ordered them implemented in time for the midterm elections. 

Unless Republicans efforts to challenge the new maps in federal court are successful, Democrats look poised to pick up several seats in the Philadelphia suburbs. So we'll start there and move westward through the new districts. 
The biggest Republican loser in the redrawn maps: Rep. Ryan Costello. 
    His winding, Chester County-based district was already a top Democratic target. But he's a moderate incumbent with strong fundraising figures, so he was the slight favorite for re-election. That's no longer the case. The new 6th District voted in favor of Hillary Clinton over President Donald Trump by 10 percentage points in 2016, and given Democrats' surge in suburbia in recent state and special elections across the country, this territory could be even more favorable to Democratic challenger Chrissy Houlahan this fall. This district now leans in Democrats' favor. 
    Freshman Rep. Brian Fitzpatrick is another Republican already locked in a tough re-election in the Philadelphia suburbs. His Bucks County-based district didn't change much, but now incorporates a more left-leaning portion of Montgomery County than it had before. What's now the 1st District favored Clinton by 2 points. Fitzpatrick's district, which previously was rated lean Republican, is now a toss-up. 
    One Philadelphia-area seat Republicans are almost certain to lose is the new 5th District, an area previously represented in part by Rep. Pat Meehan, a Republican retiring amid a sexual harassment scandal. The district favored Clinton by an eye-popping 26 points in 2016. For now, we'll rate it likely Democratic while we wait to see if Republicans can recruit someone to make this a race.
    Another major shift came in the new Pennsylvania 7th District, an altered version of the Lehigh Valley district where Republican Rep. Charlie Dent is retiring. Previously favorable ground for the GOP, it's now an open seat that voted in Clinton's favor by a point in 2016 and leans Democratic. 
    The biggest Republican winner under the new maps is Rep. Lloyd Smucker, whose seat now appears safe. His Lancaster-based district, which now becomes the 11th District, moves from a likely Republican rating, which reflected the reality that it was a longshot Democratic target, to a solid Republican rating.
    Democratic Rep. Matt Cartwright's northeastern Pennsylvania territory becomes the new 8th District. Even though it favored Trump in 2016, Cartwright is an established, well-funded incumbent, and his seat maintains a likely Democratic rating.

    Western Pennsylvania

    The new congressional map also has the potential to shake things up in the western part of the state.
    It won't take effect before the March 13 special election in the 18th District, vacated by former GOP Rep. Tim Murphy. Democrat Conor Lamb is currently within striking distance of Republican state Rep. Rick Saccone in a district that Trump carried by 20 points in 2016.
    The 18th District will, with some tweaks, become the 14th District under the new map. The redrawn district appears to be more favorable terrain for Republicans.
    However, that means that the newly formed 17th District, just west of Pittsburgh, would present a more appealing opportunity for Lamb, win or lose in March. Should he run there, he would likely challenge GOP Rep. Keith Rothfus, who currently represents what's been much safer turf for Republicans than the new 17th District, which went narrowly for Trump in 2016 and includes suburban areas that have recently been favorable terrain for Democrats.
    The new 17th District moves from a solid Republican rating to lean Republican for now, with a Lamb bid having the potential to push it into toss-up territory.
    Our ratings account for an oddity of Pennsylvania's new political reality, with the previous maps having a last hurrah in the March special election: The current 18th District is still in place, and still carries a lean Republican rating. As soon as that election takes place, though, it'll drop from our ratings, with the new 14th District appearing to be solidly Republican.