The poll showed support for Clinton at 44 percent, with Sanders close behind at 42 percent. This represents an enormous change since the previous national Quinnipiac poll in December, which showed Clinton beating Sanders 61 percent to 30 percent.
It also represents a significant departure from most recent national polling, which has suggested Clinton holds a comfortable lead among Democratic voters even though Sanders came within a percentage point of victory in the Iowa caucuses and is a clear favorite in New Hampshire polls. TPM's PollTracker average shows Clinton leading Sanders nationally by 50.3 percent to 37.6 percent.
The Quinnipiac poll was carried out from Feb. 2-4 by live telephone interview. Pollsters surveyed 484 likely Democratic voters with a margin of error of 4.5 percentage points.