From the Wall Street Journal/NBC poll (PDF link). 19 points is more than the 15 point margin Dems had when they took back the Congress in 2006:
Question 12 (on page 18 of the poll): What is your preference for the outcome of this year's congressional elections--a Congress controlled by Republicans or a Congress controlled by Democrats?
Republican-controlled Congress....... 33
Democrat-controlled Congress ......... 52
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