Charlie Cook's analysis:
Come November, Senate Democrats' 60-vote supermajority is toast. It is difficult, if not impossible, to see how Democrats could lose the Senate this year. But they have a 50-50 chance of ending up with fewer than 55 seats in the next Congress.
As for the House, we at The Cook Political Report are still forecasting that Democrats will lose only 20 to 30 seats. Another half-dozen or more retirements in tough districts, however, perhaps combined with another party switch or two, would reduce Democrats' chances of holding the House to only an even-money bet. We rate 217 seats either "Solid Democratic" or "Likely Democratic," meaning that the GOP would have to win every single race now thought to be competitive to reach 218, the barest possible majority. But if Democrats suffer much more erosion in their "Solid" and "Likely" columns, control of the House will suddenly be up for grabs.