Former Vice President Al GoreAlbert (Al) Arnold GoreJoe Lieberman: We’re well beyond partisanship, our national government has lost civility Trump doesn't start a trade war, just fires a warning shot across the bow Dems face hard choice for State of the Union response MORE today warned that Democrats could see another candidate fall just short of the White House if supporters do not work hard to push Barack ObamaBarack Hussein ObamaOvernight Energy: Dems ask Pruitt to justify first-class travel | Obama EPA chief says reg rollback won't stand | Ex-adviser expects Trump to eventually rejoin Paris accord Overnight Regulation: Trump to take steps to ban bump stocks | Trump eases rules on insurance sold outside of ObamaCare | FCC to officially rescind net neutrality Thursday | Obama EPA chief: Reg rollback won't stand Ex-US ambassador: Mueller is the one who is tough on Russia MORE toward victory between now and Nov. 4

Gore sent an e-mail to MoveOn.org supporters this afternoon, urging them to volunteer for Obama's campaign and using 2000 as a cautionary tale.

"Barack Obama is rising up to unite America behind his vision of progressive change. Yet we know from 2000 that progress is not inevitable. Victory can fall just out of reach. And the difference of a few thousand votes can put our country on a decidedly different path," Gore wrote.

"That's why I'm writing to you today to personally ask you to volunteer with the Obama campaign to help get out the vote this week. Everything we've worked for together hangs in the balance in these next few days," the former vice president continued.

Gore has largely stayed out of the limelight of the 2008 campaign aside from his highly publicized endorsement of Obama in June.