Former Vice President Joe Biden has been steadily losing support since he announced his 2020 presidential bid last April.

The percentage of Democratic voters who'd be satisfied with a Biden presidency has been on a steady decline, dropping from a high of 71% last February to 56% in October, according to Insider polling.

During the same period, support for a Warren presidency among Biden backers has steadily risen from 42% last December to 57% in October. Sen. Elizabeth Warren is the candidate favored by the highest percentage of Biden supporters, by far.

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Former Vice President Joe Biden has been steadily shedding support since he announced his 2020 presidential bid last April — and he's losing ground to Sen. Elizabeth Warren.

The number of self-identified Democratic primary voters who'd be satisfied with a Biden presidency has been on a steady decline, dropping from a high of 71% last February to 56% in October, according to Insider polling.

Read more: How the INSIDER 2020 Democratic primary tracker works

Meanwhile, the number of Democrats who'd be unsatisfied if Biden were to win the nomination has jumped since early this year. That number has approximately doubled from about 14% in January to 27% in October.

During the same period, support for a Warren presidency among Biden backers has steadily risen from 42% last December to 57% in October. Among Biden supporters, Warren is by far the candidate favored by the highest percentage of Biden supporters, by far.

Warren gained momentum over the summer, slightly overtaking Biden in a key Iowa poll last month.

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And at the same time, Biden supporters are much more likely now than they were earlier this year to support other candidates, in addition to the vice president. On average, Biden supporters like 3.5 other candidates in the race last January. Today, that number has jumped to 4.5.

By comparison, Warren supporters backed 4.4 candidates in the first month of the year, and now they back 4.9 on average. That's a slight gain — to be expected in general, as the primary inherently leads to cross-contamination of candidates by its very nature — but the Biden jump being double Warren's should give the former vice president pause.

This isn't to say that Biden is specifically losing support to Warren, just more that the people who a frontrunner should have locked down right now are increasingly open-minded and have strongly positive sentiments about Warren.

They may still very well be Biden supp porters, were we to ask about who they support most in the primary, or who they would vote for if the primary were held tomorrow. But the votes aren't for months, and this sentimental shift in Warren's direction spells nothing but trouble for the race to come.