(CNN) First things first: The theme song of the week is Mork & Mindy closing credits .

A new Quinnipiac University poll out this week finds Sen. Elizabeth Warren with a 74% favorable rating and a 10% unfavorable rating among potential Democratic primary voters. Her favorable rating is up significantly from 61% in May , while her unfavorable rating is down from 16%.

This poll is one of many that suggests Warren's favorable rating has climbed since the beginning of the year.

Warren seems to have the hot hand in the Democratic presidential primary. She's challenging former Vice President Joe Biden for the lead in Iowa, New Hampshire and nationally. These numbers show that at least part of her rise is because she's become more popular.

However, her growing popularity does not seem to be extending to outside the Democratic base.

Quinnipiac was kind enough to provide me with a crosstab of how non-potential Democratic voters (i.e. those who are not Democrats or Democratic-leaning independents) feel about Warren.

This month, she comes in with an 11% favorable rating and a 70% unfavorable rating among this group. That shouldn't be too surprising, given that, while some of this group are independents who don't lean toward either party, much of it is made up of Republicans and Republican-leaning independents. We simply should expect Warren (or any Democrat) to struggle with this group.

What's interesting is the trendline. Back in Quinnipiac's May poll, Warren's favorable rating with non-potential Democratic primary voters was 8%, compared to an unfavorable rating of 66%. A CNN poll a month later put Warren with an 11% favorable and 66% unfavorable rating with this group.

Put another way, Warren has not really seen any improvement with non-potential Democratic primary voters over the summer, even as she has dramatically improved with Democrats.

Now compare Warren's numbers with that of her chief Democratic rival, Biden. He's become considerably less popular with Democrats. His favorable rating with potential Democratic primary voters from May to now has gone from 79% to 72% and his unfavorable has gone from 14% to 19%.

Among non-potential Democratic voters, the fall off has not been as dramatic. Biden's favorable rating remains steady at 22%. His unfavorable rating is up from 63% in May to 70% now.

Biden maintains a clear edge in net favorability (favorable - unfavorable) rating of -48 points versus -59 points for Warren among non-potential Democratic primary voters.

Biden's advantage here may explain why he does better in polls against Republican President Doanld Trump than Warren. A recent Fox News poll , for instance, had both Biden and Warren beating Trump -- but Biden more than doubled Warren's margin over the President (14 points vs. 6 points). He did so, in large part, because he did significantly better than Warren among non-Democratic primary voters.

Of course, we'll have to see how this week's impeachment news may shift these numbers. Biden's numbers could slink southward as Republicans attack him.

But for now, Biden's maintaining his electability edge over Warren.