In the next two weeks, Democratic leaders will review new polls and other data that show whether vulnerable incumbents have a path to victory. If not, the party is poised to redirect money to concentrate on trying to protect up to two dozen lawmakers who appear to be in the strongest position to fend off their challengers.

“We are going to have to win these races one by one,” said Representative Chris Van Hollen of Maryland, chairman of the Democratic Congressional Campaign Committee, conceding that the party would ultimately cut loose members who had not gained ground…

While Democrats have all but given up hope that the political or economic climate will improve substantially before the election, they are not conceding control of the House. Several party leaders and strategists privately acknowledge that about 20 seats are already probably lost, but they believe they can build a fire wall around seats in the Northeast and in other pockets across the country where Republicans have nominated untested candidates.

The battle is boiling down to a question of mathematics and difficult decisions for Democrats. By the best-case Democratic calculation, party strategists believe that Republicans must beat about 35 sitting Democrats if the parties split 16 highly competitive open seats and Democrats win four of five Republican seats they see as within their reach in Delaware, Florida, Hawaii, Illinois and Louisiana.