Even though Sen. Bernie Sanders put their primary rivalry behind him and campaigned hard for Hillary Clinton, the former secretary of state lost in Wisconsin, Michigan and New Hampshire, all hard-core Sanders states. The two are pictured here in Raleigh, North Carolina, Nov. 3, 2016. Brian Snyder/Reuters

Sen. Bernie Sanders, who gave Hillary Clinton a serious challenge during the primaries, appeared to take a swipe at the former secretary of state on Thursday, saying the party cannot cozy “up to Wall Street.

Sanders, who describes himself as a Democratic socialist, urged Democrats in a tweet to side with working families, forsaking the campaign dollars that flow from special interests and billionaires.

During the primary, Sanders hammered at the Clinton fundraising machine and criticized her paid speeches to the likes of Goldman Sachs.

Clinton won the popular vote, but Republican Donald Trump won more than the 270 Electoral College votes needed to secure the presidency.

The appeal came one day after Sanders issued a statement indicating he was willing to give the president-elect a chance.

“Donald Trump tapped into the anger of a declining middle class that is sick and tired of establishment economics, establishment politics and the establishment media,” Sanders said.

“To the degree that Mr. Trump is serious about pursuing policies that improve the lives of working families in this country, I and other progressives are prepared to work with him.”

Like Trump, Sanders appealed to disaffected voters, in his case the young who feel their path to success is blocked by a lethargic economy. Trump appealed to older workers, lost by technology and international trade agreements. Both were seen as outsiders who could shake up the system.

Though Sanders campaigned for Clinton, she lost biggest in the states where he dominated in the primaries, including Michigan, Wisconsin and New Hampshire, indicating voters were not willing to give up their “Bernie or Bust” mentality.

Sanders told the Associated Press Clinton’s loss was embarrassing, saying the “Democratic message of standing up for working people no longer holds much sway among workers in this country.” He attributed the election results to a “lack of enthusiasm” that kept down voter turnout.

FBI Director James Comey’s decision to reopen the investigation of Clinton’s private email server barely a week before the voting may have also caused irreparable damage.

Pundits had thought the Republican party would face a civil war following the election. Instead, it’s the Democrats who need to figure out what was lacking.

Clinton’s loss to Trump created a leadership vacuum in the Democratic party, rocked by the release of its emails by hackers who turned them over to WikiLeaks. With the loss, the party has a chance to rebuild, and Sanders wants that rebuilding to include a change in focus.

"Bernie supporters warned the party — and they would not listen. Win or lose, the party elite blew this," Jonathan Tasini, a former Sanders surrogate, emailed reporters before the race was called, NBC News reported.