This article reminds me of the analysis I did a while back on VPs who subsequently run for president. Sounds like the track record for mid-term appointees to the Senate is similar to that for VPs who try to move up a seat:

[New York Governor] Paterson kept talking and displayed why he is fast gaining a reputation as a governor who’s not only forthright and smart, but refreshingly analytical:

Interestingly enough, I was reading that there have been, there have been, I think in the last century, over 80 times when governors have had to appoint senators. And since 1960, there have been 48. Of the 48, 10 have just decided to serve out the term and not run for election. Of the 38 that ran for election, only 18 won. So, less than half actually won. So, as I think about that, because of the precious nature of seniority in Washington, I’m hoping that a candidate that I select would win in 2010. Because what’s very key in the U.S. Senate, and what the U.S. senators that I’ve spoken to have apprised me, is that seniority is very important.

I believe the going rate for re-election of sitting U.S. senators is about 90 percent. So, if Paterson’s reading of history is correct, a less-than-50 percent re-election rate for this subset of incumbents would seem to be a pretty good indication that they were pretty unimpressive. By announcing this fact, Paterson may have just made his own task a bit harder, but he sounds wise enough to handle it.

On that basis, the Republicans may well have a better shot than thought at the Illinois senate seat when the appointee comes up for re-election.