Lisa Murkowski, who has decided to run a write-in campaign for the Senate, may soon have some company. Representative Mike Castle, the moderate Delaware Republican who was upended by Christine O’Donnell in the primary, is also said to be considering a write-in bid. Although both Mr. Castle and his advisers have characterized a bid as unlikely, his interest is serious enough that he’s commissioned a poll, according to reporting by Politico.
I discussed Ms. Murkowski’s chances chances last week and came to the conclusion that her write-in bid had a legitimate chance at succeeding. Our forecasting model — going off some thin polling and some tenuous assumptions, puts those chances at 17 percent, which seems reasonable enough.
Mr. Castle’s situation is comparable with Ms. Murkowski’s in some ways. A Public Policy Polling survey put Mr. Castle’s favorability rating at 44 percent among Delaware likely voters, against 40 percent unfavorable. That’s broadly similar to the approval rating that the same pollster found for Ms. Murkowski; they had 50 percent of Alaskans approving of her performance as Senator and 43 percent disapproving. (Although approval ratings and favorability ratings are not quite the same thing, the numbers are similar to one another more often than not.)
In other ways, though, the dynamics of the race are different:
* Mr. Castle has a considerably smaller pool of independent voters to draw from. In 2008 exit polling, 21 percent of Delaware voters identified as independent, one of the lower percentages in the country, and about half the 43 percent who did so in Alaska.
* Mr. Castle could receive a decent number of Democratic votes. Polling that pitted him head-to-head in a (now hypothetical) one-on-one matchup against the Democratic nominee, Chris Coons, had shown him getting about one-third of the Democratic vote. On the other hand, Mr. Coons has perhaps become a little bit more entrenched than the Democrat in Alaska, Scott McAdams, simply because — in contast to Mr. McAdams — Mr. Coons had become the overwhelming favorite to win his race the moment that Ms. O’Donnell became the nominee. There may be an element of loss aversion among Democratic supporters of Mr. Coons, who could be less likely to support Mr. Castle in practice than they might have been in theory.
* Among Republicans, Ms. O’Donnell is a weaker candidate than Mr. Miller. While Mr. Miller has committed some gaffes and may be too conservative for some voters, there are not persistent questions about his fitness for office, as there are in Ms. O’Donnell’s case. Still, a candidate as polarizing as Ms. O’Donnell is, by definition, going to have her share of strong supporters, and voters who have declared their intention to support her in spite of a week’s worth of terrible headlines might not be so quick to abandon her now.
The other difference between Delaware and Alaska, of course, is that while there are considerably more Republicans than Democrats in Alaska, the reverse is true in Delaware, where Democrats outnumbered Republicans 48 percent to 31 percent in 2008. Although those numbers will be narrowed in a midterm year in which Republican enthusiasm appears to outpace that of Democrats, Democrats should still constitute the plurality of Delaware’s electorate, probably by some margin.
I tried to model the three-way race and came up with the following: Mr. Coons with 37 percent of the vote, Mr. Castle with 34 percent, and Ms. O’Donnell with 29 percent.

That, obviously, would imply a winnable race for Mr. Castle — although it assumes that he is fairly serious about his write-in bid. Mr. Castle is 71 years old and has not faced too many competitive elections in recent years, and he took his time to enter the Senate race last year after considering retiring from politics entirely, so this is far from a sure thing.
One dynamic that may be more favorable to Mr. Castle is that it seems conceivable he could win with as little as 35 percent of the vote. It seems probable to me that Ms. O’Donnell’s support is going to hover in the area of 30 percent — not a lot higher, not a lot lower — which was about the percentage of voters who had a favorable impression of her in the Public Policy Polling survey. That would leave Mr. Castle and Mr. Coons to fight over the remaining 70 percent of the electorate, making half that total — 35 percent — the magic number.
In contrast, given the number of conservative voters in Alaska, it’s hard to see Mr. Miller finishing with less than about 40 percent of the vote, which would create a higher burden for Ms. Murkowski to meet. She could win if the support of the Democrat, Scott McAdams, were to collapse, with a likely result of about Ms. Murkowski 41, Mr. Miller 40, and Mr. McAdams 19. But it’s a more uphill climb.
The other contingency in Delaware is that Ms. O’Donnell is very unlikely to win a two-way race, whereas Mr. Miller in Alaska probably would have won his. I don’t really buy that an enthusiasm gap might make Ms. O’Donnell’s race against Mr. Coons dramatically more competitive than the polling would suggest; a CNN poll, which gave Mr. Coons a 16-point lead among likely voters, gave him a 25-point lead among registered voters. In other words, the polling is already implying a quite substantial enthusiasm gap in Ms. O’Donnell’s favor, and she is losing fairly badly in spite of that.
Interestingly, Mr. Castle could actually improve Ms. O’Donnell’s chances of winning by taking more of Mr. Coons’s vote than hers. Her chances have nowhere to go but up, after all. But if my suspicion is right that Ms. O’Donnell’s support is capped at not much more than 30 percent of the vote in a three-way race, she would need support to be almost exactly evenly divided among the three candidates at 33 percent each to have a chance. Perhaps a three-way recount would be the most suitable way to end this election cycle.