When the Republican John Sununu defeated Jeanne Shaheen six years ago in a bitter Senate race in New Hampshire, he had one distinct advantage over the former Democratic governor: the support of an overwhelmingly popular wartime president, George W. Bush.

Today, Mr Sununu, a member of a Republican dynasty, faces a rematch against Ms Shaheen in November and is considered the most vulnerable Republican incumbent in a field of Senate races that strongly favour Democrats.