Real Clear Politics now rates 133 Democratic held seats as safe. That means 123 Democratic held seats are in play, almost half of the current total. The number in play rises every few days. Seats move from Safe Democratic to Likely Democratic, or Likely Democratic to Lean Democratic, or Lean Democrat to Tossup, or Tossup to Lean Republican.
This does not mean that the GOP will pick up 123 seats. But RCP now rates the GOP as ahead in 211 races, the Democrats ahead in 185, and 39 tossups. A split of the tossups would give the GOP, 230 or 231, a gain of 51 or 52 net seats, and control with a bit to spare. With the RCP generic ballot edge for the Republicans at around 7%, the possibility of a sweep with gains of 70-80 seats becomes more of a possibility, though by no means likely, at least not yet. Many races remain very close. The Democratic Party is pulling previously committed cash infusions from candidates now deemed doomed, and sending the money to help incumbents thought safe a few week back. This is further evidence of the widening playing field.