In recent years, it hasn't been hard for House campaign committee officials to identify their list of most vulnerable members on the other side of the aisle. Going after Republicans representing Democratic-leaning suburbs has been a key element of the Democratic Congressional Campaign Committee's strategy to win control of the House. Likewise, the National Republican Congressional Committee is accustomed to pursuing moderate Democrats with relish.
But this year, the game is different. After three consecutive wave elections, the House caucuses have become much more ideologically homogenous: There simply aren't many Democrats left representing the rural, conservative heartland or, conversely, many Republicans in the inner suburbs. Blue Dog Democrats are struggling to remain relevant, having lost more than half of their members to last year's midterms and others, such as Rep. Dan Boren (D-Okla.) to retirement.