Warren maintains her lead despite a small likability gap. Fifty-two percent of likely voters have a favorable opinion of Brown, compared to 33 percent who view him unfavorably. Warren's numbers are more mixed: 47 percent favorable, versus 37 percent unfavorable.

But Warren continues to outpace Brown on two key measures. By a 43-percent-to-35-percent margin, voters say Warren "will stand up for people when in the Senate," and Warren leads by 6 points when voters are asked which candidate agrees with them "on key issues."