Democracy Corps/GQR: Clinton +11

[pbrower2a]

Generic congressional ballots are useless junk.

No, they aren't. They may not always be the most accurate, but they have given us a good idea of what the House PV would be.

In a D+4 election, the Democrats win the House. In 2010 the Republicans established many districts with R+2, R+3, and R+4 advantages and very few with D+1 top D+5 advantages.  Democrats got very sure seats. The slightly-R seats would have been tailor-made for moderate Republicans, but the Republicans elected pols better suited for R+30 districts.

Gerrymandering obviously can't help Republicans in the Senate.

[pbrower2a]

Retention rates are high when politicians fit their districts well.  But let the district change, and a venerable Congressional Representative becomes vulnerable.  Let a district go from majority-Anglo to majority Hispanic, as happened to Bob Dornan, and the right-wing Republican gets replaced by Loretta Sanchez, a liberal. The electoral results for his district slowly deteriorated for him.

Elected incumbents can lose. Some causes include

1. being in the job only for oneself.
2. misuse of the perquisites of office (like hiring lots of family members as staff)
3. scandals (mercifully rare)
4. not being up to the job (which may include deterioration of performance)
5. poor constituent service, like being unresponsive to them
6. being out of touch with the interests of constituents

Most Congressional representatives do nothing to get ousted. But the political environment can change.