Poll: Sanders, Biden seen as most popular second choices in Dem primary

Former Vice President Joe BidenJoe Robinette BidenBiden calls for unity, jabs at Trump in campaign launch Here are the potential candidates still eyeing 2020 bids Warren policy ideas show signs of paying off MORE and Sen. Bernie SandersBernie SandersHere are the potential candidates still eyeing 2020 bids Sanders unveils education plan that would ban for-profit charter schools Warren policy ideas show signs of paying off MORE (I-Vt.) are the most popular potential Democratic presidential candidates, but they are also the top second choices among registered voters, according to a Morning Consult survey released this week.

The poll found that Sanders was the second choice for 27 percent of Biden's supporters. Another 15 percent of Biden supporters said they would back Sen. Kamala HarrisKamala Devi HarrisHere are the potential candidates still eyeing 2020 bids Warren policy ideas show signs of paying off Hillicon Valley: Florida county that backed Trump was one of two hacked by Russians | Sandberg pushes back on calls to break up Facebook | Conservative groups ask WH to end Amazon talks over Pentagon contract MORE (D-Calif.) while 9 percent said they supported Sen. Elizabeth WarrenElizabeth Ann WarrenHere are the potential candidates still eyeing 2020 bids Sanders unveils education plan that would ban for-profit charter schools Warren policy ideas show signs of paying off MORE (D-Mass.).

Among Sanders's supporters, 26 percent said they supported Biden as a second choice, followed by Warren at 16 percent and Harris at 7 percent.

Warren and Sanders both hail from the progressive wing of the Democratic Party, while the poll showed some crossover between those supporting Biden and Harris.

Among Harris's supporters, 20 percent said they would choose Biden as a second choice, while Sanders was not among the top picks as a backup option. And among Biden supporters, 15 percent said they would support Harris as a second choice.

However, Sanders registered strongly as a second choice for Warren's supporters, with 25 percent saying the Vermont senator and 2016 runner-up for the Democratic nomination was a backup for them, followed by Harris at 14 percent and Biden at 13 percent.

Among former Rep. Beto O'RourkeBeto O'RourkeOvernight Health Care — Presented by Campaign for Accountability — Momentum builds for federal laws enshrining abortion rights | Missouri lawmakers approve bill banning abortions at 8 weeks | Warren unveils plan to protect abortion rights Overnight Energy: Dems dismiss Interior chief's work calendars as 'fake' | Buttigieg climate plan includes carbon tax | Poll finds growing number say climate is crucial 2020 issue Buttigieg climate plan includes carbon tax MORE's (D-Texas) supporters, 20 percent said they would pick Sanders as a second option, while 18 percent chose Biden. 

O'Rourke has yet to announce whether he will run for president next year, though has been mulling a bid.

The poll comes as speculation around potential 2020 runs from Biden and Sanders heats up. 

The Hill reported on Thursday that sources familiar with the former vice president's plans say that he is almost certain to enter the 2020 fray.  

Yahoo News reported late last month that Sanders would announce his second presidential bid in the near future.

Warren formally launched her White House bid last weekend, while Harris entered the race late last month.

The Morning Consult poll was conducted from Feb. 4-10 among 11,627 registered voters. The survey's margin of error is plus or minus 1 percent. 

— Julia Manchester