In his 30-plus years of handicapping House, Senate and governor races, Stuart Rothenberg has generally been pretty cautious. In this recent blog post, however, he steps out of form. “I am now expecting a substantial Republican Senate wave in November, with a gain of at least seven seats. … But I wouldn’t be shocked by a wider margin.”

Rothenberg inserts appropriate caveats. His newsletter’s current ratings, based on current polling, show a Republican gain of six seats — what they need for a Senate majority — as likely but by no means certain. And as he notes, if President Obama’s job approval should suddenly rise, Republicans’ chances of gaining six or seven states would be sharply reduced. Still, he’s willing to predict a seven-seat-plus “wave.” His reasoning: