Tomorrow’s primaries in New York and six other states — the last of the 2010 cycle, save for Saturday’s primary in Hawaii and a runoff in Louisiana on Oct. 2 — originally looked as though they’d have little impact on the electoral landscape. Although some of the primaries were nominally competitive – like the Republican Senate race in Maryland, where a suite of 11 candidates will be on the ballot — they were typically not so in places where the nominee stood a strong chance of winning the general election.
Two races, however, have changed that equation. And depending on how they are resolved, Republican chances of taking over the Senate could be enhanced or significantly diminished.
But then a strange thing happened. Joe Miller, who had the backing of Sarah Palin and the Tea Party Express, upended the incumbent Lisa Murkowski in the Republican Senate primary in Alaska. Although the outcome arguably should not have been such a surprise – a dearth of polling concealed whatever momentum Mr. Miller might have been gaining – it emboldened Tea Party activists and some other conservatives, who were reminded that in this topsy-turvy electoral cycle, few incumbents and establishment politicians are safe. Mr. Castle — a moderate who is unambiguously a member of the establishment – was next on their target list. And so Ms. O’Donnell, who already had the support of the Tea Party, last week received endorsements from Republican thought-leaders like Ms. Palin, the National Rifle Association and Senator James DeMint of South Carolina.
In contrast to Alaska, however, where Mr. Miller is the favorite to be elected unless Ms. Murkowski finds her way onto the ballot as a Libertarian or write-in candidate, Delaware is a blue state, and the electoral prospects of Mr. Castle and Ms. O’Donnell there are wildly divergent. Whereas Mr. Castle is nearly a 95 percent favorite against the Democratic nominee, Chris Coons, according to last week’s FiveThirtyEight forecasting model, Ms. O’Donnell would have just a 17 percent chance of winning a race against Mr. Coons.
The primaries in Delaware and New Hampshire have implications far beyond their borders. The forecast model that we ran last week gave Republicans a 26 percent chance of taking over the Senate — and enough states are tossups that they would be well within reach of doing so if the elections were held today. But this forecast was based on a weighted average likelihood of various candidates winning their primaries — for example, we had estimated that Ms. O’Donnell had a 25 percent chance of prevailing in Delaware, and Mr. Lamontange a 30 percent chance of doing so in New Hampshire — leaving Mr. Castle and Ms. Ayotte as the favorites.
If Ms. O’Donnell and Mr. Lamontange were both to win their primaries, however, the Republican chances of a Senate takeover would fall to just 16 percent, according to the model. Conversely, if Mr. Castle and Ms. Ayotte were to win, Republicans chances would rise to 30 percent. Thus, Republican prospects of claiming the Senate could be nearly halved if both the insurgent candidates were to prevail.
