A spokeswoman for Sen. Bernie Sanders Bernie SandersSirota reacts to report of harassment, doxing by Harris supporters Republicans not immune to the malady that hobbled Democrats The Hill's Morning Report - Sponsored by Facebook - Republicans lawmakers rebuke Trump on election MORE (I-Vt.) on Thursday said that many of the progressive senator’s fellow 2020 contenders will have to answer for their past stances on various issues.

“A lot of candidates are going to have to answer for their histories — both in office and before they joined political office,” Briahna Joy Gray, told Hill.TV.

Gray did not mentions any candidates by name, but said she's not worried about Sanders, saying his “longevity is a selling point instead of something that you have to excuse.”

“We have a candidate who has been in office so, so long and yet at the same time doesn’t have all of those foibles,” she told Hill.TV, citing his long-standing support of civil rights.

Sanders is behind in the polls to former Vice President Joe Biden Joe BidenFormer Pence aide: White House staffers discussed Trump refusing to leave office Progressive group buys domain name of Trump's No. 1 Supreme Court pick Bloomberg rolls out M ad buy to boost Biden in Florida MORE, whose past stance on the Iraq War and the 1994 crime bill have both come under attention. Biden also took criticism from Sen. Kamala Harris Kamala HarrisTexas Democratic official urges Biden to visit state: 'I thought he had his own plane' The Hill's Campaign Report: Biden on Trump: 'He'll leave' l GOP laywers brush off Trump's election remarks l Obama's endorsements A game theorist's advice to President Trump on filling the Supreme Court seat MORE (D-Calif.), another presidential hopeful, during the first presidential debate for his past opposition to federal busing of students.

Sanders will take the debate stage tonight in Houston at Texas Southern University alongside Biden and fellow progressive Sen. Elizabeth Warren Elizabeth WarrenOvernight Defense: Appeals court revives House lawsuit against military funding for border wall | Dems push for limits on transferring military gear to police | Lawmakers ask for IG probe into Pentagon's use of COVID-19 funds On The Money: Half of states deplete funds for Trump's 0 unemployment expansion | EU appealing ruling in Apple tax case | House Democrats include more aid for airlines in coronavirus package Warren, Khanna request IG investigation into Pentagon's use of coronavirus funds MORE (D-Mass.). Those three candidates have been leading most recent national polls, along with surveys in Iowa and New Hampshire.

—Tess Bonn