Recent national polls show Democrats with an advantage on the generic ballot ranging from 3 to 6 points. That is larger than the Democrats’ 2-point advantage in the October 2012 NBC News-Wall Street Journal poll (when Democrats gained eight seats) or the Democrats’ 4-point advantage in the October 2014 poll (when the GOP gained 13 seats).

However, large Democratic waves in 2006 and 2008 followed October NBC News-Wall Street Journal polls that showed Democrats with a generic advantage of 15 points and 13 points respectively — advantages not close to the current numbers.

Democratic operatives acknowledge that their fight for 30 seats is decidedly uphill, pointing to “structural disadvantages” given the way districts are drawn. But they argue that undecided voters profile as Democratic, and they remain optimistic about gains in suburban districts, open seats and states like California, Nevada and Florida.

In contrast, Republican insiders appear confident about their party’s ability to retain control of the House. But they also acknowledge that many questions remain and that a small shift can turn a 51 percent-49 percent victory into a 51 percent-49 percent loss.