A couple people inquired about this piece I posted yesterday, forecasting potential electoral outcomes in U.S. House races this fall. I reported on a recent analysis by Jim Ellis of PRIsm Information Network. Ellis notes that only 18 House races fall into the “up for grabs” category that could go either way this November (he categorizes the remaining 415 districts as either “safe, likely, or lean” toward one party or the other). Some readers wanted to know the partisan and incumbency breakdown (whether the incumbent is running for reelection or if it is an open seat) of those 18 seats.

The 18 toss-up districts break right down the middle in terms of party control--9 Republicans and 9 Democrats. That’s the good news for Republicans. But the incumbent/open seat mix tilts heavily in favor of Democrats. I reorganized Ellis’s district list below, breaking it down by party and incumbency. Political parties always have a better shot at holding a district where an incumbent is running, compared to an open seat where the incumbent is retiring. Some research suggests that incumbents begin with about a 10-point advantage, all other things equal. As Fred Barnes noted this week, the Republicans’ dim prospects of retaking the House in 2008 contributed to many of these retirement decisions, which in turn leads to the self-fulfilling prophesy of an ongoing Democrat majority.

Here is the GOP's challenge:

Democrat Open Seats:
AL-5 (Rep. Cramer retiring)

Republican Open Seats:
AZ-1 (Rep. Renzi retiring)
NJ-3 (Rep. Saxton retiring)
NJ-7 (Rep. Ferguson retiring)
NM-1 (Rep. Wilson retiring)
OH-15 (Rep. Pryce retiring)
OH-16 (Rep. Regula retiring)

Democrat Incumbent Running:
AZ-5 (Rep. Mitchell)
FL-16 (Rep. Mahoney)
KS-2 (Rep. Boyda)
NH-1 (Rep. Shea-Porter)
PA-10 (Rep. Carney)
PA-11 (Rep. Kanjorski)
TX-22 (Rep. Lampson)
WI-8 (Rep. Kagan)

Republican Incumbent Running
AK-AL (Rep.Young)
NC-8 (Rep. Hayes)
NV-3 (Rep. Porter)