The New York Times today ran this analysis of the campaign for Congress. The trend, as in the presidential election, is in favor of the Democrats.
As I wrote here, the Democrats' goal is to reach 60 Senate seats. That is the number of votes needed to end a filibuster, which would be the only major remaining weapon for Republicans to block legislation if, as the polls currently indicate, both houses of Congress and the White House end up under Democratic control.
One analysis cited in the Times article describes the high end of the Democratic range as being a gain of nine seats. That would get them to 60, if the two New England independents, Joe Lieberman and Bernie Sanders, are included. I discussed Lieberman's situation here.
The question of needing Lieberman for the Democrats' 51-49 majority is somewhat different than that of needing his vote to end a filibuster. The filibuster question will apply separately to each individual issue. Since Lieberman is generally in agreement with the Democrats on domestic policy, chances are they can usually count on his vote on a cloture motion.