washington president barack obama thursday urge 25,000 volunteer advocate dial white house conference call pull stop boost number people sign obamacare health insurance plan obama warn challenge overcome skepticism plan give onslaught headline surge premium price say stake high think critical time show program work people see options tell volunteer work communities encourage assist enrollment americans receive health insurance employer medicare medicaid program shop online subsidize insurance plan start nov. end january average premium benchmark 2017 plan sell healthcare.gov rise 25 percent compare 2016. obama say tax credit help seven 10 shoppers get plan less 75 per month say many may bother look hear spike cost go clear bug windshield people see road ahead guy come obama say law fight republicans congress say create unwarranted government intervention personal healthcare private industry several big insurers include unitedhealth group inc unh.n aetna inc aet.n humana inc hum.n pull online marketplaces sell subsidize plan cite bigger-than-expected financial losses aetna chief executive mark bertolini say thursday early company may return marketplaces would 2019. obama say young healthy people need sign plan would offset insurers cost cover members serious illnesses obama say series improvements could make signature domestic policy achievement 2010 affordable care act congress next president take office jan. 20 work together part time overcome skeptics prove people wrong provide momentum next administration come start position strength obama tell conference call obama rally obamacare troop 'critical time program