There are many districts, in different states, who barely elected republican congressmen, in 2010, with 50%-51% of the vote. The majority of those districts usually elect Democrats, so some of those Republicans will lose. However, Rep. Walsh is running in a district where the majority of the voters are Republicans. The majority of the state senators, state reps., and county commissioners, from his district, are Republicans.
You are mistaken. Very few seats we gained in 2010 were democrat leaning seats. Most were GOP leaning seats that went democrat in the bad elections of 2006 or 2008 or had been democrat long term but conservative, always voting GOP for President and long overdue to elect a Republican Congressman or were usually close swing seats.
The only democrat leaning we seats we gained were
Bobby Schilling in IL-17, he would have probably won again under the old lines but under the new even worse lines he could lose, polls have been tight.
Cravaack in MN-8, while democrat leaning this area is becoming more Republican. He may lose. Ironically he is the first Republican to win that seat since 1944, in 1946 we lost it even while winning a huge landslide nationwide.
Bass in NH 1, The more democrat of the 2 New Hampshire seats. He may lose.
Buerkle in NY-25 (now 24th), Her seat was made even worse and she will probably lose
PA-7 and PA-8, both were made better in redistricting and the incumbents are not in any danger this time.
Barletta in PA-11, this was the most democrat seat we gained but, it’s been redrawn and is now GOP leaning! He is no danger.
Farenthold in TX-27, also redrawn and is now a safe Republican seat.
So that is only 8 democrat leaning seats we gained out of 66 total gains (against 3 losses, all in democrat seats).
And of those 8 gained seats, only 4 are at risk in this election.
Of course there are many other seats we could lose like some of the many swing seats we won and a few we will lose for sure like MD-1 which was redraw to be democrat but redistricting overall was a gain for us.
I predict we will break even, at worst.