(CNN) It's now safe to say that Massachusetts Sen. Elizabeth Warren is rivaling Vermont Sen. Bernie Sanders for second place in the fight for the Democratic nomination.

And her rise can be tied to her populist policy driven campaign. Interestingly, however, she isn't winning over working-class voters.

While polls do differ somewhat, Warren's 15% to Sanders' 14% in a new national Monmouth University poll matches the general finding of most polls . Warren has risen from the mid-single digits in March to the low-to-mid-double digits today, while Sanders has dropped from the low 20s to about 15%.

Warren has historically scored her best when voters are asked who they think has the best policy plans. A Quinnipiac University poll taken in late April found that 19% of voters believed Warren had the best policy plans. On the question of who voters thought was the most likely to beat Trump, just 3% of Democratic primary voters said Warren.

This finding repeats itself in state polls as well: Warren's best scores came on policy. In a Quinnipiac Pennsylvania poll for example, 18% of Democratic voters said Warren had the best policy plans. When it came to who was the most likely to beat Trump, only 3% of Pennsylvania Democrats said Warren.

Warren's strength on policy differentiates her from Biden. Biden consistently scored in the 50s when asked which candidate was the most likely to beat Trump. Biden polled in the 20s and usually just ahead of Warren when voters were asked who had the best policy plans.

You can see that Warren's focus on policy has paid off with voters in another way. Warren does her best amongst those paying the most attention to the campaign. That is, she's likely benefiting from the media pointing out how she's running her campaign.

In a Quinnipiac poll last week, Warren earned 17% of the vote among those paying a lot of attention to the campaign. She was at 6% among those paying little to no attention to the campaign. Sanders, with whom Warren is battling with for very liberal voters, saw the exact opposite pattern. He was at 9% among those paying a lot of attention and a significantly higher 36% among those paying little-to-no attention.

Here's another way Warren and Sanders differ: Warren's populist rhetoric is appealing most to white collar voters, not the blue collar voters many of her policies are directed toward.

Take a look at the most recent Monmouth poll. Warren earns 23% among those with a college degree and only 11% among those without a college degree. For Sanders, the pattern is reversed. He does 8 points better among those without a college degree than voters with a college degree.

Another way to examine the same phenomenon is to look at how voters along the income spectrum are voting. In the most recent Quinnipiac poll, Warren got 20% among those earning $50,000 or more per year. Her support was half that (10%) among those earning less than $50,000. Again this was different than Sanders whose support dropped as voter income rose.

Warren's pattern of support seems to be following a traditional track in the sense that the most liberal candidates tend to get their highest support among white collar voters. This was the case for Howard Dean in 2004, for example.

Sanders is actually the odd duck in that he was the more liberal candidate who often did his best among working class voters. In 2016, just like now, he got more support among non-college educated whites and whites who earned less money.

For Warren to ultimately succeed in 2020, she'll need to start winning over some of those blue collar voters. If she continues to be a populist candidate of only the white collar voter, she won't win the nomination.