A longtime congressional stronghold for Republicans, Pennsylvania is emerging in dramatic fashion as a source of hope for Democrats in their quest to take control of the U.S. House in November's mid-term elections. 

This week cemented Democratic victories in two key battles: Republicans dropped talk of legal challenges to Democrat Conor Lamb's improbable victory in a special election in southwestern Pennsylvania and federal courts rejected two GOP lawsuits seeking to block a state court-drawn map of more competitive districts. 

For years, Pennsylvania has hosted one of the nation's biggest Republican congressional delegations.  Now, what had been a 13-to-5 Republican advantage in Pennsylvania's 18-member delegation could get wiped out. 

It's been seven head-spinning months. 

First, five Republican congressmen decided not to run again, including one — suburban Pittsburgh's Tim Murphy — who resigned last October amid a sex scandal.  Those openings created opportunities for Democrats. 

Then the state Supreme Court, ruling in a gerrymandering lawsuit, junked Pennsylvania's six-year-old district boundaries that were drawn by Republicans to get Republicans elected.  The court's Democratic majority redrew the boundaries, improving Democrats' chances in five districts in particular. 

Amid all that, Pennsylvania was the nation's political hot spot for a few weeks while Lamb and Republican Rick Saccone competed to fill the remainder of Murphy's term.  Party strategists viewed the March 13 special election as a test of Republican strength while President Donald Trump is a divisive force. 

Lamb's narrow victory in a district that Trump won by nearly 20 percentage points over Hillary Clinton in 2016's presidential election sent shivers down Republican spines everywhere as the primary season unfolds. 

Avalanche of candidates

By Tuesday night's deadline, 94 people filed signatures to get on May 15's primary election ballot in Pennsylvania's congressional districts.  That's more than twice the number who appeared on 2016's primary ballot. 

Of those, 59 are Democrats and 35 are Republicans. 

Endangered Republicans

The redrawn districts overhauled a map in which Trump won 12 of Pennsylvania's 18 districts — one of them by a fraction of a percentage point — in 2016.  Under the new map, Trump would have won 10. 

Republican and Democratic strategists agree that three Republican congressmen face serious challenges: second-term Ryan Costello, freshman Brian Fitzpatrick and third-term Keith Rothfus. 

Costello, who has privately told party brass that he may not run, is in dire straits. 

Under the discarded map, Costello's suburban Philadelphia district had a Republican majority that nevertheless helped Clinton beat Trump there by 2 percentage points in 2016.  The redrawn district has slightly more Democrats and Clinton would have won it by 9 percentage points.  Democratic challenger Chrissy Houlahan is considered one of the top 33 challengers nationwide by the Democratic Congressional Campaign Committee. 

Fitzpatrick's district was already a swing district, and the court's boundaries made it slightly tougher for a Republican.  It now has about 10,000 more Democrats and Clinton would have won it by 2 percentage points.  Three Democrats filed petitions to challenge him. 

Rothfus' 100-mile-long district in western Pennsylvania was redrawn into a tight shape in suburban Pittsburgh.  A rock-solid conservative district that Trump won by nearly 21 percentage points is now considered a tossup.  Compounding the bad news for Rothfus is that Lamb lives in the district and filed to run there, although Lamb still faces a three-way primary race. 

The tossup district

Retiring Republican Rep. Charlie Dent's 80-mile-long district in eastern Pennsylvania was redrawn back into its longtime Allentown-area territory and is considered a tossup.  Six Democrats and two Republicans filed to run there. 

Flipping a district

Now that he isn't running again, Republican Rep. Pat Meehan's seat is expected to fall into Democratic hands.  The district — nicknamed "Goofy Kicking Donald Duck" for its contorted boundaries snaking through four counties that Republicans drew to save Meehan from Philadelphia's increasingly liberal suburbs — was compressed back into its historic Delaware County base.  Clinton would have won it by 28 percentage points. 

With that in mind, an eye-popping 14 Democrats filed to run there.  Delaware County's Democratic Party chairman David Landau said he couldn't predict who would win. 

For years, the party struggled to find good candidates to challenge Meehan, Landau said. 

"Since Donald Trump became president, no more," Landau said. " Since redistricting, we found even more good candidates."