Congressional Republicans are facing a historic deficit on the generic ballot

(CNN)Democrats keep looking for signals that the Republicans are in trouble.

They look to special elections. They looked to the primary results from Texas, which are not a great predictor of the fall results.
But folks, there's a easy way to know the Republicans are in trouble: just ask the voters.
Republicans are performing at a historic low on the generic congressional ballot.
    An average of live interview surveys since February 1 shows that the Democrats are beating the Republicans by a 48% to 38% margin. This 10-point margin matches the average from surveys released on Wednesday by Monmouth University and Quinnipiac University.
    It's difficult to overstate what a poor position that is for the party that holds the House majority.
    As I have done previously, I gathered all the generic ballot polls I could at this point in the midterm cycle since 1938, a far larger data set than is usually available for examining either special elections or primary turnout. Excluding 1970, for which we have no data, no majority party have ever trailed by more than 10 points on the generic ballot at this point in the cycle.
    The only other time a majority party faced a deficit of 10 points was in 2006, when Republicans controlled the House and Senate.
    Democrats, who were the minority party in 2006 as they are in 2018, would go on to take control of both chambers of Congress later that year. Democrats are far ahead of where they were in either 2010 or 2014, when the generic ballot was essentially tied at this point.
    And Democrats are doing well consistently. I performed this same exercise with generic ballot at different points during this cycle. At each point that I looked, Democrats were doing as well or better than any minority party had done previously.
    The Democratic lead on the generic ballot right would probably be enough for Democrats to take back the House if it holds.
    Democrats will need to do better than merely winning the House popular vote to gain a majority of seats. Determining where the exact threshold is for Democrats being likely to take back the House is a little difficult. Using different methodologies will lead you to slightly different answers.
    But even with a fairly conservative estimate based off of the lean of each individual district, Democrats probably need to win the House by around 7 points to have a net gain of 24 seats to take back the House.
    Their 10-point lead in the average poll since the beginning of February is larger than that. The advantage is more consistent with a net seat gain in the mid 30s than the mid 20s.
    Now, of course, things can change as head towards November. But the two main reasons the generic ballot has shifted historically don't apply to the Democrats and their lead right now.
    Democrats don't control the White House (the generic ballot tends to shift against the party which holds the presidency). Also, the Democratic lead isn't above 10 points in the average of polls (usually there is a reversion to the mean for very large leads.)
    Still, a shift necessary for the Republicans to keep control of the House is well within the margin of error, even after controlling for these two main sources of error.
    If someone was trying to project control of the House based off the generic ballot at this time, it would be best to say it titled toward the Democrats: A race where Democrats would win more times than not, though one that Republicans could definitely win.