This is unlikely to be a direct re-run of the 1966 election for House and Senate. (This illustration is of the 1966 House races, from Wikipedia. Note the biggest Republican swings were in the Midwest.)
It's going to be much, much worse for Republicans than that.
In 1966 Democrats lost 48 House seats and only 3 Senate seats. Such a result this time would give them a healthy House majority neutered by a Senate minority.
In that year, Democrats tried very hard to make Republicans the issue. They called them dangerous. They called them warmongers. They linked them to Joe McCarthy and Herbert Hoover. The trouble was both were dead.
Republicans this year at least have live villains. The problem is the claims don't pass the smell test. And anger against the Bush Administration is becoming palpable. As angry as Republican rhetoric may be, Democratic rhetoric is angrier, and this is a new phenomenon. Even the Republican "Munich" argument is finally getting some serious push-back.