So says Nate Silver:
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. They would still have a chance of doing so — but it might require them to expand the playing field further, such as to West Virginia or Connecticut, where the Democratic candidates are clear favorites but not prohibitive ones – or to perform a quick makeover on a candidate like Ms. O’Donnell, who is unlikely to make a good first impression with moderate and independent voters.
Surely, those dynamics could change if a victorious Lamontagne and O’Donnell ran smart general election campaigns that appealed to disaffected Democrats and independents. But that’s a big if.